Magnetic tape cartridge and magnetic recording and reproducing device

ABSTRACT

In the magnetic tape, in a case where a maximum value of an absolute value of a difference between a servo band spacing obtained before storage in an environment of a temperature of 32° C. and relative humidity of 55% and a servo band spacing obtained after storage in the environment for a storage time T is set to A, and T is defined as 24 hours, 48 hours, 72 hours, 96 hours, or 120 hours, a medium life calculated by a linear function of A and a logarithm logeT of T, that are derived from a value of A and a value of the logarithm logeT of T obtained for each T is 3 years or longer. The medium life is T in a case where the A satisfies Equation 1: A=1.5−B.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2021-076851 filed on Apr. 28, 2021. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape cartridge and amagnetic recording and reproducing device.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for variousdata storage (for example, see JP6590102B).

SUMMARY OF THE INVENTION

The recording of data on a magnetic tape is normally performed bycausing the magnetic tape to run in a magnetic recording and reproducingdevice (normally referred to as a “drive”) and causing a magnetic headto follow a data band of the magnetic tape to record data on the databand. Accordingly, a data track is formed on the data band. In addition,in a case of reproducing the recorded data, the magnetic tape is causedto run in the magnetic recording and reproducing device and the magnetichead is caused to follow the data band of the magnetic tape, therebyreading data recorded on the data band. After such recording orreproducing, the magnetic tape is stored while being wound around a reelin a magnetic tape cartridge (hereinafter, referred to as a “cartridgereel”), until the next recording and/or reproducing is performed.

During the recording and/or the reproducing is performed after thestorage, in a case where the magnetic head for recording and/orreproducing data records and/or reproduces data while being deviatedfrom a target track position due to deformation of the magnetic tape,phenomenons such as overwriting on recorded data, reproducing failure,and the like may occur. Meanwhile, in recent years, in the field of datastorage, there is an increasing need for long-term storage of data,which is called an archive. However, in general, as a storage periodincreases, the magnetic tape tends to be easily deformed. Therefore, itis expected that suppression of the occurrence of the above phenomenonafter storage will be further required in the future.

In view of the above, an object of an aspect of the invention is toperform recording and/or reproducing in an excellent manner duringrecording and/or reproducing of data with respect to the magnetic tapeafter accommodation and storage in a magnetic tape cartridge.

According to an aspect of the invention, there is provided a magnetictape cartridge comprising: a magnetic tape which is wound around acartridge reel (hereinafter, also simply referred to as a “reel”) andaccommodated in the magnetic tape cartridge, in which the magnetic tapeincludes a non-magnetic support, and a magnetic layer containing aferromagnetic powder, the magnetic layer includes a plurality of servobands, in a case where a maximum value of an absolute value of adifference between a servo band spacing obtained before storage in anenvironment of a temperature of 32° C. and relative humidity of 55% anda servo band spacing obtained after storage in the environment for astorage time T is defined as A, a unit of A is μm, and T is set to 24hours, 48 hours, 72 hours, 96 hours, or 120 hours, a medium lifecalculated by a linear function of A and a logarithm log_(e)T of T, thatare derived from a value of A and a value of the logarithm log_(e)T of Tobtained for each T (hereinafter, also referred to as a “medium life”)is 3 years or longer, the medium life is T, in a case where A satisfiesEquation 1:

A=1.5−B, and   (Equation 1)

the B is a value calculated by multiplying a difference between amaximum value and a minimum value of the servo band spacings obtained ineach of the following five environments of a temperature of 16° C. andrelative humidity of 20%, a temperature of 16° C. and relative humidityof 80%, a temperature of 26° C. and relative humidity of 80%, atemperature of 32° C. and relative humidity of 20%, and a temperature32° C. and relative humidity of 55%, by ½, and the unit is μm.

In one embodiment, the T in a case where the A calculated by the linearfunction satisfies Equation 1 may be 3 years to 150 years.

In one embodiment, the magnetic tape may further include a non-magneticlayer containing a non-magnetic powder between the non-magnetic supportand the magnetic layer.

In one embodiment, the magnetic tape may further include a back coatinglayer containing a non-magnetic powder, on a surface side of thenon-magnetic support opposite to a surface side provided with themagnetic layer.

In one embodiment, the non-magnetic support may be an aromatic polyestersupport.

In one embodiment, the aromatic polyester support may be a polyethyleneterephthalate support.

In one embodiment, the aromatic polyester support may be a polyethylenenaphthalate support.

In one embodiment, the non-magnetic support may be an aromatic polyamidesupport.

In one embodiment, a vertical squareness ratio of the magnetic tape maybe 0.60 or more.

According to another aspect of the invention, there is provided amagnetic recording and reproducing device comprising the magnetic tapecartridge.

In one embodiment, the magnetic recording and reproducing device mayfurther comprise a magnetic head having a reproducing element width of0.8 μm or less.

In one embodiment, the magnetic recording and reproducing device mayfurther comprise: the magnetic tape cartridge; and a winding reel, inwhich the magnetic tape is caused to run between the winding reel and acartridge reel of the magnetic tape cartridge in a state where a tensionis applied in a longitudinal direction of the magnetic tape, where amaximum value of the tension is 0.50 N or more, and the magnetic tapeafter running in the state where the tension is applied is wound aroundthe cartridge reel of the magnetic tape cartridge by applying a tensionof 0.40 N or less in the longitudinal direction of the magnetic tape.

According to one aspect of the invention, it is possible to performrecording and/or reproducing in an excellent manner during recordingand/or reproducing of data with respect to the magnetic tape afteraccommodation and storage in the magnetic tape cartridge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a magnetic recordingand reproducing device.

FIG. 2 is a perspective view of an example of a magnetic tape cartridge.

FIG. 3 is a perspective view in a case where the magnetic tape isstarted to be wound around a reel.

FIG. 4 is a perspective view in a case where the magnetic tape has beenwound around the reel.

FIG. 5 shows an example of disposition of data bands and servo bands.

FIG. 6 shows a servo pattern disposition example of a linear-tape-open(LTO) Ultrium format tape.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One aspect of the present invention relates to the above magnetic tapecartridge.

In addition, another aspect of the invention relates to a magneticrecording and reproducing device including the above magnetic tapecartridge.

The magnetic tape cartridge includes a magnetic tape and a cartridgereel. In an unused magnetic tape cartridge that has not yet beenattached to a magnetic recording and reproducing device for datarecording and/or reproducing, the magnetic tape is typicallyaccommodated while being wound around a cartridge reel. In the magneticrecording and reproducing device, the magnetic tape can run between thecartridge reel (supply reel) and the winding reel to record data on themagnetic tape and/or reproduce the recorded data. After the recording orreproducing of data, the magnetic tape is rewound around the cartridgereel, and stored while being wound around the cartridge reel in themagnetic tape cartridge, until the next recording and/or reproducing isperformed.

It is surmised that different deformations occur depending on theposition such that, during the storage, in the magnetic tapeaccommodated in the magnetic tape cartridge, a part near the cartridgereel is deformed wider than the initial stage due to compressive stressin a tape thickness direction, and a part far from the cartridge reel isdeformed narrower than the initial stage due to the tensile stress inthe tape longitudinal direction. It is considered that, in a case wherethe significant different deformations occur depending on the position,this may cause the magnetic head to record and/or reproduce data whilebeing deviated from the target track position, in a case where therecording and/or the reproducing is performed after storage.

The inventors considered that the deformation includes a deformationmainly occurring due to stress received during the storage, and adeformation mainly occurring due to a temperature and humidity in anenvironment in which data recording and/or reproducing is performed(hereinafter, referred to as a “use environment”). During the intensivestudies of the inventors, the inventors considered that considering thedeformations occurring due to the above factors in a comprehensive wayenables excellent recording and/or reproducing in the data recordingand/or reproducing with respect to the magnetic tape after accommodationand storage in the magnetic tape cartridge. As a result of furtherstudies, the inventors came to adopt the medium life as a comprehensiveindicator related to the deformation caused by the above factors, andnewly found that, according to the magnetic tape cartridge having amedium life of 3 years or longer, the excellent recording and/orreproducing can be performed in the data recording and/or reproducingwith respect to the magnetic tape after accommodation and storage in themagnetic tape cartridge.

Hereinafter, the magnetic tape cartridge and the magnetic recording andreproducing device will be described more specifically. Hereinafter, oneembodiment of the magnetic tape cartridge and the magnetic recording andreproducing device may be described with reference to the drawings.However, the magnetic tape cartridge and the magnetic recording andreproducing device are not limited to the embodiment shown in thedrawings. In addition, the present invention is not limited to theinference of the inventors described in the present specification.

Medium Life

A method for measuring the medium life described above will be describedbelow.

Procedure for Deriving Linear Function Measurement of Servo Band Spacing

In order to derive Equation 1 for calculating A, various servo bandspacings are measured by the following methods.

The servo band spacing before the storage is measured in a measurementenvironment of an atmosphere temperature of 23° C. and relative humidityof 50%. The magnetic tape cartridge to be measured is placed in anenvironment of an atmosphere temperature of 23° C. and a relativehumidity of 50% for 5 days in order to make it familiar with theenvironment for measurement.

After that, in this measurement environment of an atmosphere temperatureof 23° C. and a relative humidity of 50%, in a magnetic recording andreproducing device including a tension adjusting mechanism for applyinga tension in the longitudinal direction of the magnetic tape, themagnetic tape is allowed to run in a state where a tension of 0.70 N isapplied in the longitudinal direction of the magnetic tape. For suchrunning, the spacing between two servo bands adjacent to each other witha data band interposed therebetween is measured at spacing of 1 m overthe entire length of the magnetic tape. In the measurement for obtainingvarious values described in the invention and the specification, a valueof the tension applied in the longitudinal direction of the magnetictape is a set value set in the magnetic recording and reproducingdevice. In addition, in the invention and the specification, to describe“measurement at spacing of 1 m”, in a measurement target region having alength of L meters (m), in a case where a length of a position of oneend of the measurement target region is set to 0 m and a length of eachposition in a direction facing the other end is set to 1 m, 2 m, 3 m, .. . , and a length of a position of the other end is set to L m, aninitial measurement position is a position of 1 m and a finalmeasurement position is one position before the position of L m. Inaddition, in a case where there are a plurality of servo band spacings,the servo band spacing is measured in the same manner for all servo bandspacings. The servo band spacing measured in this way is referred to asa “servo band spacing before storage” at each measurement position.

After that, the magnetic tape cartridge is stored for 24 hours in astorage environment of an atmosphere temperature of 32° C. and arelative humidity of 55%.

After the storage, after the magnetic tape cartridge is left in themeasurement environment of an atmosphere temperature of 23° C. and arelative humidity of 50% for 5 days in order to make it familiar withthe measurement environment, in the same measurement environment, in amagnetic recording and reproducing device including a tension adjustingmechanism for applying a tension in the longitudinal direction of themagnetic tape, the magnetic tape is allowed to run in a state where atension of 0.70 N is applied in the longitudinal direction of themagnetic tape. For such running, the servo band spacing is measured inthe same manner as in the method described above. The servo band spacingmeasured in this way is referred to as a “servo band spacing afterstorage for 24 hours” at each measurement position.

For the all servo band spacing, a difference between the servo bandspacing before the storage and the servo band spacing after the storagemeasured at spacing of 1 m is obtained. By doing so, a plurality ofdifference values are obtained. A maximum value of an absolute value ofthe obtained difference is defined as “A after storage for 24 hours”.The unit of A is μm. This point is the same for the following variousA's.

The spacing between two servo bands adjacent to each other with the databand interposed therebetween can be obtained by using, for example, aposition error signal (PES) obtained from a servo signal obtained byreading a servo pattern with a servo signal reading element. Fordetails, the description of examples which will be described later canbe referred to.

The magnetic tape cartridge after measuring the servo band spacing afterthe storage for 24 hours is stored in a storage environment of anatmosphere temperature of 32° C. and a relative humidity of 55% for 48hours.

After the storage, after the magnetic tape cartridge is left in themeasurement environment of an atmosphere temperature of 23° C. and arelative humidity of 50% for 5 days, in the same measurementenvironment, in a magnetic recording and reproducing device including atension adjusting mechanism for applying a tension in the longitudinaldirection of the magnetic tape, the magnetic tape is allowed to run in astate where a tension of 0.70 N is applied in the longitudinal directionof the magnetic tape. For such running, the servo band spacing ismeasured in the same manner as in the method described above. The servoband spacing measured in this way is referred to as a “servo bandspacing after storage for 48 hours” at each measurement position.

For the all servo band spacing, a difference between the servo bandspacing before the storage and the servo band spacing after the storagemeasured at spacing of 1 m is obtained. By doing so, a plurality ofdifference values are obtained. A maximum value of an absolute value ofthe obtained difference is defined as “A after storage for 48 hours”.

The magnetic tape cartridge after measuring the servo band spacing afterthe storage for 48 hours is stored in a storage environment of anatmosphere temperature of 32° C. and a relative humidity of 55% for 72hours.

After the storage, after the magnetic tape cartridge is left in themeasurement environment of an atmosphere temperature of 23° C. and arelative humidity of 50% for 5 days, in the same measurementenvironment, in a magnetic recording and reproducing device including atension adjusting mechanism for applying a tension in the longitudinaldirection of the magnetic tape, the magnetic tape is allowed to run in astate where a tension of 0.70 N is applied in the longitudinal directionof the magnetic tape. For such running, the servo band spacing ismeasured in the same manner as in the method described above. The servoband spacing measured in this way is referred to as a “servo bandspacing after storage for 72 hours” at each measurement position.

For the all servo band spacing, a difference between the servo bandspacing before the storage and the servo band spacing after the storagemeasured at spacing of 1 m is obtained. By doing so, a plurality ofdifference values are obtained. A maximum value of an absolute value ofthe obtained difference is defined as “A after storage for 72 hours”.

The magnetic tape cartridge after measuring the servo band spacing afterthe storage for 72 hours is stored in a storage environment of anatmosphere temperature of 32° C. and a relative humidity of 55% for 96hours.

After the storage, after the magnetic tape cartridge is left in themeasurement environment of an atmosphere temperature of 23° C. and arelative humidity of 50% for 5 days, in the same measurementenvironment, in a magnetic recording and reproducing device including atension adjusting mechanism for applying a tension in the longitudinaldirection of the magnetic tape, the magnetic tape is allowed to run in astate where a tension of 0.70 N is applied in the longitudinal directionof the magnetic tape. For such running, the servo band spacing ismeasured in the same manner as in the method described above. The servoband spacing measured in this way is referred to as a “servo bandspacing after storage for 96 hours” at each measurement position.

For the all servo band spacing, a difference between the servo bandspacing before the storage and the servo band spacing after the storagemeasured at spacing of 1 m is obtained. By doing so, a plurality ofdifference values are obtained. A maximum value of an absolute value ofthe obtained difference is defined as “A after storage for 96 hours”.

The magnetic tape cartridge after measuring the servo band spacing afterthe storage for 96 hours is stored in a storage environment of anatmosphere temperature of 32° C. and a relative humidity of 55% for 120hours.

After the storage, after the magnetic tape cartridge is left in themeasurement environment of an atmosphere temperature of 23° C. and arelative humidity of 50% for 5 days, in the same measurementenvironment, in a magnetic recording and reproducing device including atension adjusting mechanism for applying a tension in the longitudinaldirection of the magnetic tape, the magnetic tape is allowed to run in astate where a tension of 0.70 N is applied in the longitudinal directionof the magnetic tape. For such running, the servo band spacing ismeasured in the same manner as in the method described above. The servoband spacing measured in this way is referred to as a “servo bandspacing after storage for 120 hours” at each measurement position.

For the all servo band spacing, a difference between the servo bandspacing before the storage and the servo band spacing after the storagemeasured at spacing of 1 m is obtained. By doing so, a plurality ofdifference values are obtained. A maximum value of an absolute value ofthe obtained difference is defined as “A after storage for 120 hours”.

The inventors consider that the value of A obtained as described abovecan be an indicator related to the deformation mainly occurring due tothe stress that the magnetic tape receives during the storage in themagnetic tape cartridge.

Derivation of Linear Function

In the step described above, the value of A is obtained for the fivetypes of storage time T. From these values of A and the logarithmlog_(e) T of the storage time T, a linear function of A and log_(e) T isderived by the least squares method. The linear function is representedby Y=cX+d, where A is Y and log_(e)T is X. c and d are coefficientsdetermined by the least squares method, respectively, and usually both cand d are positive values.

Procedure for Determining B

B used to obtain the medium life is a value determined by the followingmethod.

B is a value (unit: μm) calculated by multiplying a difference between amaximum value and a minimum value of the servo band spacings obtained ineach of the following five environments of a temperature of 16° C. andrelative humidity of 20%, a temperature of 16° C. and relative humidityof 80%, a temperature of 26° C. and relative humidity of 80%, atemperature of 32° C. and relative humidity of 20%, and a temperature32° C. and relative humidity of 55%, by ½. B is obtained by thefollowing method.

For each measurement environment, the magnetic tape cartridge to bemeasured is placed in the measurement environment for 5 days in order tomake it familiar with the measurement environment. The measurementenvironments are the five environments described above (that is,temperature of 16° C. and relative humidity of 20%, temperature of 16°C. and relative humidity of 80%, temperature of 26° C. and relativehumidity of 80%, temperature of 32° C. and relative humidity of 20%, andtemperature of 32° C. and relative humidity of 55%).

After that, in the measurement environment, in a magnetic recording andreproducing device including a tension adjusting mechanism for applyinga tension in the longitudinal direction of the magnetic tape, themagnetic tape is allowed to run in a state where a tension of 0.70 N isapplied in the longitudinal direction of the magnetic tape. Regardingthe magnetic tape, an end on a side wound around a reel of the magnetictape cartridge is referred to as an inner end, an end on the oppositeside thereof is referred to as an outer end, the outer end is set to 0m, and in a region of a length of 0 m to 100 m (hereinafter, referred toas a “region having a reel outer periphery of 100 m”), a servo bandspacing is measured at spacing of 1 m in a data band 0 (zero) in therunning at spacing of 1 m. The “data band 0” is a data band defined bythe standard as a data band in which data is first embedded (recorded).An arithmetic mean of the measured servo band spacings is the servo bandspacing in the measurement environment.

After obtaining the servo band spacing in each of the five environmentsas described above, a value calculated as “(maximum value−minimumvalue)×½” using the maximum value and the minimum value among theobtained values is defined as “B” of the magnetic tape cartridge to bemeasured. The inventors consider that B obtained as described above is avalue that can be an indicator of deformation that mainly occurs due tothe temperature and humidity of the use environment.

Calculation of Medium Life

The medium life is a value calculated as T in a case where A satisfies“Equation 1: A=1.5−B” by the linear function of the A and the logarithmlog_(e) T of T derived above. The inventors consider that the mediumlife calculated above which is 3 years or longer, that is, the time T atwhich A +B is 1.5 μm is 3 years or longer means that a total deformationamount of the deformation mainly occurring due to the stress receivedwhile the magnetic tape is stored in the magnetic tape cartridge and thedeformation mainly occurring due to the temperature and humidity of theuse environment is unlikely to increase over a long period of time. Thereason for setting 1.5 μm and 3 years as threshold values is inconsideration of the needs for long-term storage and high-densityrecording that will be desired in the future. Regarding the medium life,1 year is 365 days. Therefore, 1 year is 365×24 hours=8760 hours. Inaddition, 0.5 years is 6 months and 1 month is 30 days. Therefore, 0.5years is 6×30×24 hours=4320 hours. The various measurement environmentsdescribed above are examples, and the magnetic tape cartridges are notlimited to those stored and/or used in the exemplified environment.

From a viewpoint of enabling excellent recording and/or reproducing inthe recording and/or reproducing of data with respect to the magnetictape after being accommodated and stored in the magnetic tape cartridge,the medium life of the magnetic tape cartridge is 3 years or longer,preferably 10 years or longer, and more preferably in order of 20 yearsor longer, 30 years or longer, 40 years or longer, 50 years or longer,60 years or longer, 70 years or longer, 80 years or longer, 90 years orlonger, and 100 years or longer. The medium life of the magnetic tapecartridge can be, for example, 200 years or shorter, 190 years orshorter, 180 years or shorter, 170 years or shorter, 160 years orshorter, 150 years or shorter, 140 years or shorter, 130 years orshorter, or 120 years or shorter, and can also exceed the valuesexemplified here. A method for controlling the medium life will bedescribed later.

The value of B of the magnetic tape cartridge can be, for example, 0.0μm or more, more than 0.0 μm, 0.05 μm or more, or 0.1 μm or more, andfor example, 2.0 μm or less, 1.5 μm or less, or 0.5 μm or less. However,the magnetic tape cartridge may have a medium life of 3 years or more,and the value of B is not limited to the above range.

Configuration of Magnetic Recording and Reproducing Device

FIG. 1 is a schematic view showing an example of a magnetic recordingand reproducing device.

A magnetic recording and reproducing device 10 shown in FIG. 1 controlsa recording and reproducing head unit 12 in accordance with a commandfrom a control device 11 to record and reproduce data on a magnetic tapeMT.

The magnetic recording and reproducing device 10 has a configuration ofdetecting and adjusting a tension applied in a longitudinal direction ofthe magnetic tape from spindle motors 17A and 17B and driving devices18A and 18B which rotatably control a cartridge reel 130 and a windingreel 16.

The magnetic recording and reproducing device 10 has a configuration inwhich the magnetic tape cartridge 13 can be mounted.

The magnetic recording and reproducing device 10 includes a cartridgememory read and write device 14 capable of performing reading andwriting with respect to the cartridge memory 131 in the magnetic tapecartridge 13.

An end portion or a leader pin of the magnetic tape MT is pulled outfrom the magnetic tape cartridge 13 mounted on the magnetic recordingand reproducing device 10 by an automatic loading mechanism or manuallyand passes on a recording and reproducing head through guide rollers 15Aand 15B in the direction in which a surface of a magnetic layer of themagnetic tape MT comes into contact with a surface of the recording andreproducing head of the recording and reproducing head unit 12, andaccordingly, the magnetic tape MT is wound around the winding reel 16.

The rotation and torque of the spindle motor 17A and the spindle motor17B are controlled by a signal from the control device 11, and themagnetic tape MT runs at random speed and tension. A servo patternpreviously formed on the magnetic tape can be used to control the tapespeed. A tension detection mechanism may be provided between themagnetic tape cartridge 13 and the winding reel 16 to detect thetension. The tension may be adjusted by using the guide rollers 15A and15B in addition to the control by the spindle motors 17A and 17B.

The cartridge memory read and write device 14 is configured to be ableto read and write information of the cartridge memory 131 according tocommands from the control device 11. As a communication system betweenthe cartridge memory read and write device 14 and the cartridge memory131, for example, an international organization for standardization(ISO) 14443 system can be used.

The control device 11 includes, for example, a controller, a storageunit, a communication unit, and the like.

The recording and reproducing head unit 12 is composed of, for example,a recording and reproducing head, a servo tracking actuator foradjusting a position of the recording and reproducing head in a trackwidth direction, a recording and reproducing amplifier 19, a connectorcable for connecting to the control device 11. The recording andreproducing head is composed of, for example, a recording element forrecording data on a magnetic tape, a reproducing element for reproducingdata of the magnetic tape, and a servo signal reading element forreading a servo signal recorded on the magnetic tape. For example, oneor more of each of the recording elements, the reproducing element, andthe servo signal reading element are mounted in one magnetic head.Alternatively, each element may be separately provided in a plurality ofmagnetic heads according to a running direction of the magnetic tape.

The recording and reproducing head unit 12 is configured to be able torecord data on the magnetic tape MT according to a command from thecontrol device 11. In addition, the data recorded on the magnetic tapeMT can be reproduced according to a command from the control device 11.

The control device 11 has a mechanism of controlling the servo trackingactuator so as to obtain a running position of the magnetic tape from aservo signal read from a servo band during the running of the magnetictape MT and position the recording element and/or the reproducingelement at a target running position (track position). The control ofthe track position is performed by feedback control, for example. Thecontrol device 11 has a mechanism of obtaining a servo band spacing fromservo signals read from two adjacent servo bands during the running ofthe magnetic tape MT. The control device has a mechanism of adjustingand changing the tension applied in the longitudinal direction of themagnetic tape by controlling the torque of the spindle motor 17A and thespindle motor 17B and/or the guide rollers 15A and 15B so that the servoband spacing becomes a target value. The adjustment of the tension isperformed by feedback control, for example. In addition, the controldevice 11 can store the obtained information of the servo band spacingin the storage unit inside the control device 11, the cartridge memory131, an external connection device, and the like.

In the magnetic recording and reproducing device, the tension can beapplied in the longitudinal direction of the magnetic tape during therecording and/or reproducing. In the above magnetic recording andreproducing device, the tension applied in the longitudinal direction ofthe magnetic tape during the recording and/or reproducing is a constantvalue in one embodiment and changes in another embodiment. Regarding thetension in the invention and this specification, in the magneticrecording and reproducing device, the value of the tension applied inthe longitudinal direction of the magnetic tape is a value of a tensionused for controlling a mechanism in which the control device of themagnetic recording and reproducing device adjusts the tension as thetension to be applied in the longitudinal direction of the magnetictape. As described above, the tension actually applied in thelongitudinal direction of the magnetic tape in the magnetic recordingand reproducing device can be detected by, for example, providing atension detection mechanism between the magnetic tape cartridge 13 andthe winding reel 16 in FIG. 1. In addition, for example, the tension canalso be controlled by the control device or the like of the magneticrecording and reproducing device so that a minimum tension is not lessthan a value determined by a standard or a recommended value and/or amaximum tension is not greater than a value determined by a standard ora recommended value.

In one embodiment, the magnetic recording and reproducing device mayinclude a tension adjusting mechanism which adjusts a tension applied ina longitudinal direction of the magnetic tape which runs in the magneticrecording and reproducing device. The tension adjusting mechanism cancontrol the tension applied in the longitudinal direction of themagnetic tape to be variable, and preferably, can control a dimension inthe width direction of the magnetic tape by adjusting the tensionapplied in the longitudinal direction of the magnetic tape. In thetension adjustment, the tension applied in the longitudinal direction ofthe magnetic tape can be changed. An example of the magnetic recordingand reproducing device having the tension adjusting mechanism is asdescribed above with reference to FIG. 1. However, the invention is notlimited to the example shown in FIG. 1.

Magnetic Tape Cartridge

In the magnetic tape cartridge before being mounted on the magneticrecording and reproducing device and after being taken out from themagnetic recording and reproducing device, the magnetic tape isgenerally wound around the cartridge reel and is accommodated in acartridge main body. The cartridge reel is rotatably comprised in thecartridge main body. As the magnetic tape cartridge, a single reel typemagnetic tape cartridge including one reel in a cartridge main body anda twin reel type magnetic tape cartridge including two reels in acartridge main body are widely used. The magnetic tape cartridge can bea single reel type magnetic tape cartridge in one embodiment, and can bea twin reel type magnetic tape cartridge in another embodiment.Regarding the twin reel type magnetic tape cartridge, the cartridge reelrefers to a reel on which the magnetic tape is mainly wound, in a casewhere the magnetic tape is stored after recording and/or reproducingdata, and the other reel may refer to a winding reel. In a case wherethe single reel type magnetic tape cartridge is mounted in the magneticrecording and reproducing device in order to record and/or reproducedata on the magnetic tape, the magnetic tape is drawn from the magnetictape cartridge and wound around the winding reel on the magneticrecording and reproducing device, for example, as shown in FIG. 1. Amagnetic head is disposed on a magnetic tape transportation path fromthe magnetic tape cartridge to a winding reel. The magnetic tape runs byfeeding and winding the magnetic tape between the cartridge reel (alsoreferred to as a “supply reel”) on the magnetic tape cartridge and thewinding reel on the magnetic recording and reproducing device. In themeantime, for example, the magnetic head comes into contact with andslides on the surface of the magnetic layer of the magnetic tape, andaccordingly, the recording and/or reproducing of data is performed. Withrespect to this, in the twin reel type magnetic tape cartridge, bothreels of the supply reel and the winding reel are provided in themagnetic tape cartridge. In one embodiment, the magnetic tape cartridgeis preferably a single reel type magnetic tape cartridge that has beenmainly adopted in recent years in the field of data storage.

In one embodiment, the magnetic tape cartridge can include a cartridgememory. The cartridge memory can be, for example, a non-volatile memory,and tension adjustment information is recorded in advance or tensionadjustment information is recorded. The tension adjustment informationis information for adjusting the tension applied in the longitudinaldirection of the magnetic tape. Regarding the cartridge memory, theabove description can also be referred to.

FIG. 2 is a perspective view of an example of a magnetic tape cartridge.FIG. 2 shows a single reel type magnetic tape cartridge.

A magnetic tape cartridge 13 shown in FIG. 2 includes a case 112. Thecase 112 is formed in a rectangular box shape. The case 112 is generallymade of a resin such as polycarbonate. Inside the case 112, only onereel 130 is rotatably accommodated.

FIG. 3 is a perspective view in a case where a magnetic tape is startedto be wound around a reel. FIG. 4 is a perspective view in a case wherethe magnetic tape has been wound around the reel.

The reel 130 includes a cylindrical reel hub 122 that constitutes anaxial center portion.

The reel hub is a cylindrical member that configures an axial centerportion around which the magnetic tape is wound in the magnetic tapecartridge. In the magnetic tape cartridge, the reel hub can be asingle-layer cylindrical member or can be a multi-layered cylindricalmember having two or more layers. From viewpoints of manufacturing costand ease of manufacturing, the reel hub is preferably a single-layercylindrical member.

The inventors consider that the high stiffness of the reel hub aroundwhich the reel is wound in the magnetic tape cartridge is preferable inorder to increase the value of the medium life. This is due to thefollowing reasons.

It is considered that, in a case where the magnetic tape is wound, thereel hub receives a winding force in a center direction and tends to bedeformed in a direction in which the diameter decreases, and it isconsidered that the reel hub having lower stiffness is more likely to bedeformed. It is surmised that, on the cartridge core side of themagnetic tape, a compressive stress is generated in a direction ofshortening a tape length so as to correspond to the deformation of thereel hub, and then a tensile stress is generated in a direction ofwidening the tape width due to the compression caused by thiscompressive stress. It is considered that the larger the stressgenerated as described above, the greater the deformation of themagnetic tape during the storage in the magnetic tape cartridge. On theother hand, in a case where the stiffness of the reel hub is high, thedeformation can be suppressed, so that the generation of the stress canbe suppressed, and it is surmised that this can contribute to anincrease of the value of the medium life. From this viewpoint, in oneaspect, a bending elastic modulus of a material constituting at least anouter peripheral side surface layer portion of the reel hub ispreferably 5 GPa or more, more preferably 6 GPa or more, even morepreferably 7 GPa or more, and still preferably 8 GPa or more. Thebending elastic modulus can be, for example, 20 GPa or less, 15 GPa orless, or 10 GPa or less. However, since the high bending elastic modulusis preferable from a viewpoint of suppressing the deformation of thereel hub, the bending elastic modulus may exceed the value exemplifiedhere.

In a case where the reel hub is the single-layer cylindrical member, thebending elastic modulus is a bending elastic modulus of the materialconstituting the cylindrical member. On the other hand, in a case wherethe reel hub is a multi-layered cylindrical member having two or morelayers, the bending elastic modulus is a bending elastic modulus of thematerial constituting at least the outer peripheral side surface layerportion of the reel hub. In the present invention and the presentspecification, the “bending elastic modulus” is a value obtainedaccording to JIS (Japanese Industrial Standards) K 7171: 2016.

JIS K 7171: 2016 is the Japanese Industrial Standard created based onISO (International Organization for Standardization) 178 and Amendment1: 2013, which was published as the 5th edition in 2010, withoutchanging the technical contents.

A test piece used for measuring the bending elastic modulus is preparedaccording to section 6 “Test piece” of JIS K 7171: 2016.

Examples of the material constituting the reel hub include a resin and ametal. Examples of the metal include aluminum. The resin is preferablefrom viewpoints of cost, productivity, and the like. Examples of theresin include fiber reinforced resins. Examples of the fiber reinforcedresin include a glass fiber reinforced resin and a carbon fiberreinforced resin. As such a fiber reinforced resin, a fiber reinforcedpolycarbonate is preferable. This is because polycarbonate is easy toprocure and can be molded with a high accuracy and at low cost by ageneral-purpose molding machine such as an injection molding machine. Inaddition, in the glass fiber reinforced resin, a content of the glassfiber is preferably 15% by mass or more. The higher the content of glassfiber, the higher the bending elastic modulus of the glass fiberreinforced resin tends to be. As an example, the content of the glassfiber of the glass fiber reinforced resin can be 50% by mass or less or40% by mass or less. In one embodiment, the resin constituting the reelhub is preferably glass fiber reinforced polycarbonate. In addition, asthe resin constituting the reel hub, a high-strength resin generallycalled a super engineering plastic or the like can be used. An exampleof a super engineering plastic is polyphenylene sulfide (PPS).

A thickness of the reel hub is preferably in a range of 2.0 to 3.0 mm,from viewpoints of satisfying both a strength of the reel hub and adimensional accuracy during molding. The thickness of the reel hub meansa total thickness of such multiple layers for a reel hub having amulti-layer structure of two or more layers. An outer diameter of thereel hub is usually determined by the standard of the magnetic recordingand reproducing device, and can be in a range of, for example, 20 to 60mm.

Flanges (lower flange 124 and upper flange 126) protruding outward in aradial direction from an upper end portion and a lower end portion ofthe reel hub 122, respectively are provided on both end portions of thereel hub 122. Here, regarding “upper” and “lower”, in a case where themagnetic tape cartridge is mounted on the magnetic recording andreproducing device, a side located above is referred to as “upper” and aside located below is referred to as “lower”. One or both of the lowerflange 124 and the upper flange 126 is preferably configured integrallywith the reel hub 122, from a viewpoint of reinforcing the upper endportion side and/or the lower end portion side of the reel hub 122. Theterm “integrally configured” means that it is configured as one member,not as a separate member. In a first embodiment, the reel hub 122 andthe upper flange 126 are configured as one member, and this member isjoined to the lower flange 124 configured as a separate member by awell-known method. In a second embodiment, the reel hub 122 and thelower flange 124 are configured as one member, and this member is joinedto the upper flange 126 configured as a separate member by a well-knownmethod. The reel of the magnetic tape cartridge may be in any form. Eachmember can be manufactured by a well-known molding method such asinjection molding.

A magnetic tape MT is wound around an outer circumference of the reelhub 122 starting from a tape inner end Tf (see FIG. 3). The reduction ofthe tension applied in the longitudinal direction of the magnetic tapein a case of winding the magnetic tape around the reel hub of thecartridge reel during the manufacture of the magnetic tape cartridge(hereinafter, also referred to as a “winding tension duringmanufacture”) also contributes to an increase in value of the mediumlife. From this point, the winding tension during manufacture ispreferably 0.40 N or less, and can also be, for example, 0.30 N or less.The winding tension during manufacture can be, for example, 0.10 N ormore or 0.20 N or more, or can be tension-free. The winding tensionduring manufacture can be a constant value or can also be changed. Thewinding tension during manufacture is a set value set in a manufacturingapparatus of the magnetic tape cartridge.

A side wall of the case 112 has an opening 114 for drawing out themagnetic tape MT wound around the reel 130, and a leader pin 116 that isdrawn out while being locked by a drawing member (not shown) of themagnetic recording and reproducing device (not shown) is fixed to a tapeouter end Te of the magnetic tape MT drawn out from this opening 114.

In addition, the opening 114 is opened and closed by a door 118. Thedoor 118 is formed in a shape of a rectangular plate having a sizecapable of closing the opening 114, and is biased by a bias member (notshown) in a direction of closing the opening 114. In a case where themagnetic tape cartridge 13 is mounted on the magnetic recording andreproducing device, the door 118 is opened against a bias force of thebias member.

A well-known technology can be applied for other details of the magnetictape cartridge. An entire length of the magnetic tape accommodated inthe magnetic tape cartridge is not particularly limited, and can be in arange of approximately, for example, 800 m to 2,500 m. The longer theentire length of the tape accommodated in one reel of the magnetic tapecartridge is, the more preferable it is from a viewpoint of increasingthe capacity of the magnetic tape cartridge.

Tension During Running and Tension During Winding on Cartridge Reel

In the magnetic recording and reproducing device, the magnetic tape canrun between the cartridge reel (supply reel) and the winding reel torecord data on the magnetic tape and/or reproduce the recorded data. Inthe magnetic recording and reproducing device described above, thetension can be applied in the longitudinal direction of the magnetictape during such running. As a greater tension is applied in thelongitudinal direction of the magnetic tape, a dimension of the magnetictape in a width direction can be more greatly contraction (that is, canbe further narrowed), and as the tension is small, a degree of theshrinkage can be reduced. Therefore, the dimension of the magnetic tapein the width direction can be controlled by the value of the tensionapplied in the longitudinal direction of the magnetic tape running inthe magnetic recording and reproducing device. In the magnetic recordingand reproducing device described above, in the one embodiment, themagnetic tape can run in a state where a tension of 0.50 N or more isapplied in the longitudinal direction at the maximum. It is consideredthat, in a case where the magnetic tape is stored in the magnetic tapecartridge as it is after running in a state where a great tension isapplied, the magnetic tape is likely to be deformed during the storage.As described above, it is surmised that different deformations occurdepending on the position such that, during the storage, in the magnetictape accommodated in the magnetic tape cartridge, a part near thecartridge reel is deformed wider than the initial stage due tocompressive stress in a tape thickness direction, and a part far fromthe cartridge reel is deformed narrower than the initial stage due tothe tensile stress in the tape longitudinal direction. It is consideredthat, in the magnetic tape accommodated in a state where a great tensionis applied, the deformations more greatly vary depending on theposition.

Therefore, in the one embodiment, in the magnetic recording andreproducing device described above, in a case where the magnetic tape iswound around the cartridge reel after the running is performed in astate where the tension of 0.50 N or more is applied in the longitudinaldirection at maximum, the tension applied in the longitudinal directionof the magnetic tape is preferably 0.40 N or less. Accordingly, theinventors have considered that, since the magnetic tape can be woundaround the cartridge reel with a tension smaller than the tensionapplied in the longitudinal direction during the running and stored inthe magnetic tape cartridge, the occurrence of a phenomenon occurred dueto the deformation described above can be further suppressed. Inaddition, the inventors have surmised that, regardless of whether or notthe tension is applied during running and the tension value, in a caseof winding the magnetic tape around the cartridge reel after running,the tension applied in the longitudinal direction of the magnetic tapeset to 0.40 N or less is preferable to further suppress the occurrenceof a phenomenon that may occur due to the deformation described above.

In a case of applying the tension in the longitudinal direction of therunning magnetic tape in the magnetic recording and reproducing device,a maximum value of the tension can be 0.50 N or more, and can also be0.60 N or more, 0.70 N or more, or 0.80 N or more. The maximum value canbe, for example, 1.50 N or less, 1.40 N or less, 1.30 N or less, 1.20 Nor less, 1.10 N or less, or 1.00 N or less. The tension applied in thelongitudinal direction of the magnetic tape during the running can be aconstant value or can also be changed. In the case of a constant value,the tension applied in the longitudinal direction of the magnetic tapecan be controlled by, for example, the control device of the magneticrecording and reproducing device so that the tension of a constant valueis applied in the longitudinal direction of the magnetic tape. On theother hand, in a case where the tension applied in the longitudinaldirection of the magnetic tape during the running is changed, forexample, the dimension information of the magnetic tape in the widthdirection during the running can be obtained using a servo signal, andthe tension applied in the longitudinal direction of the magnetic tapecan be adjusted and changed according to the obtained dimensioninformation. Accordingly, the dimension of the magnetic tape in thewidth direction can be controlled. One embodiment of such tensionadjustment is as described above with reference to FIG. 1. However, themagnetic recording and reproducing device is not limited to theexemplified embodiment. In the magnetic recording and reproducing devicedescribed above, in a case where the tension applied in the longitudinaldirection of the magnetic tape during the running is changed, theminimum value thereof can be, for example, 0.10 N or more, 0.20 N ormore, 0.30 N or more, or 0.40 N or more. In addition, the minimum valuethereof can be, for example, 0.40 N or less or less than 0.40 N in oneembodiment, and can be 0.60 N or less or 0.50 N or less in anotherembodiment.

In the magnetic recording and reproducing device, in a case where themagnetic tape runs for recording and/or reproducing data, the followingembodiment can be provided as a specific embodiment of running themagnetic tape.

Embodiment 1: At the end of running for recording and/or reproducingdata, the entire length of the magnetic tape is wound on the windingreel.

Embodiment 2: At the end of running for recording and/or reproducingdata, the entire length of the magnetic tape is wound on the cartridgereel.

Embodiment 3: At the end of running for recording and/or reproducingdata, a part of the magnetic tape is wound around the cartridge reel andanother part thereof is wound around the winding reel.

The tension in a case where the magnetic tape after running is woundaround the cartridge reel by applying tension in the longitudinaldirection of the magnetic tape (hereinafter, also referred to as“rewinding tension”) means the following tension.

In the embodiment 1, the rewinding tension is a tension applied in thelongitudinal direction of the magnetic tape, in a case where the entirelength of the magnetic tape is wound around the cartridge reel to beaccommodated in the magnetic tape cartridge.

In the embodiment 2, first, the magnetic tape is wound from thecartridge reel to the winding reel. In this case, the tension applied inthe longitudinal direction of the magnetic tape is not particularlylimited. The tension may be a constant value, may be changed, may be asin the above description regarding the value of the tension during therunning, or may be not. The tension applied in the longitudinaldirection of the magnetic tape in a case where the magnetic tape issubsequently wound around the cartridge reel is the rewinding tension.The tension is a tension applied in the longitudinal direction of themagnetic tape in a case of winding the entire length of the magnetictape from the winding reel to the cartridge reel.

The embodiment 3 can be any of the following two embodiments. In a firstembodiment (embodiment 3-1), a part of the magnetic tape that is woundaround the cartridge reel, at the end of the running for the recordingand/or the reproducing of data, is wound by applying a tension in thelongitudinal direction during the winding around the cartridge reel. Thetension during the winding is the rewinding tension. A second embodiment(embodiment 3-2) is an embodiment other than the embodiment 3-1 of theembodiment 3. In order to wind the entire length of the magnetic tapearound the cartridge reel and accommodate it in the cartridge, in theembodiment 3-1, the tension applied in the longitudinal direction of themagnetic tape, in a case where the magnetic tape is not wound around thecartridge reel is wound around the cartridge reel is the rewindingtension. The embodiment 3-2 is the same as the embodiment 2. That is,first, the magnetic tape is wound from the cartridge reel to the windingreel. The tension applied in the longitudinal direction of the magnetictape in a case of subsequently winding the entire length of the magnetictape from the winding reel to the cartridge reel is the rewindingtension.

In any of the above embodiments 1, 2 and 3, the tension (rewindingtension) applied in the longitudinal direction of the magnetic tape in acase of winding it around the cartridge reel is preferably 0.40 N orless. The rewinding tension may be a constant value or may be changed.In the one embodiment, the rewinding tension may be a constant value of0.40 N or less, or may be changed in a range of 0.40 N or less. In acase of changing, the maximum value of the tension applied in thelongitudinal direction of the magnetic tape in a case of winding itaround the cartridge reel is preferably 0.40 N or less, and can also be,for example, 0.30 N or less. The minimum value of the tension applied inthe longitudinal direction of the magnetic tape in a case of winding itaround the cartridge reel may be, for example, 0.10 N or more or 0.20 Nor more, or may be less than the value exemplified here. The tension(rewinding tension) while winding around the cartridge reel can becontrolled by, for example, the control device of the magnetic recordingand reproducing device. In addition, an operation program is recorded inthe cartridge memory so that the winding around the cartridge reel isperformed by applying the rewinding tension set after the recordingand/or reproducing of data on the magnetic tape in the longitudinaldirection of the magnetic tape, and the control device may read thisprogram to execute the winding operation.

Magnetic Tape

In the magnetic tape cartridge, the magnetic tape is wound around thecartridge reel and accommodated. Hereinafter, the magnetic tape will bedescribed more specifically.

Non-Magnetic Support

The magnetic tape includes a non-magnetic support, and a magnetic layercontaining a ferromagnetic powder. As the non-magnetic support(hereinafter, also simply referred to as a “support”), well-knowncomponents such as polyethylene terephthalate, polyethylene naphthalate,polyamide, polyamide imide, aromatic polyamide subjected to biaxialstretching are used.

In the one embodiment, the non-magnetic support of the magnetic tape canbe an aromatic polyester support. In the invention and thespecification, “aromatic polyester” means a resin including an aromaticskeleton and a plurality of ester bonds, and the “aromatic polyestersupport” means a support including at least one layer of an aromaticpolyester film. The “aromatic polyester film” is a film in which thelargest component in the component configuring this film based on massis aromatic polyester. The “aromatic polyester support” of the inventionand the specification include a support in which all of resin filmsincluded in this support is the aromatic polyester film and a supportincluding the aromatic polyester film and the other resin film. Specificexamples of the aromatic polyester support include a single aromaticpolyester film, a laminated film of two or more layers of the aromaticpolyester film having the same constituting component, a laminated filmof two or more layers of the aromatic polyester film having differentconstituting components, and a laminated film including one or morelayers of the aromatic polyester film and one or more layers of resinfilm other than the aromatic polyester. In the laminated film, anadhesive layer or the like may be randomly included between two adjacentlayers. In addition, the aromatic polyester support may randomly includea metal film and/or a metal oxide film formed by performing vapordeposition or the like on one or both surfaces. The same applies to a“polyethylene terephthalate support” and a “polyethylene naphthalatesupport” in the invention and the specification.

An aromatic ring included in an aromatic skeleton including the aromaticpolyester is not particularly limited. Specific examples of the aromaticring include a benzene ring and a naphthalene ring.

For example, polyethylene terephthalate (PET) is polyester including abenzene ring, and is a resin obtained by polycondensation of ethyleneglycol and terephthalic acid and/or dimethyl terephthalate. The“polyethylene terephthalate” of the invention and the specificationincludes polyethylene terephthalate having a structure including one ormore kinds of other components (for example, copolymerization component,and component introduced to a terminal or a side chain), in addition tothe component described above.

Polyethylene naphthalate (PEN) is polyester including a naphthalenering, and is a resin obtained by performing esterification reaction ofdimethyl 2,6-naphthalene dicarboxylate and ethylene glycol, and then,transesterification and polycondensation reaction. The “polyethylenenaphthalate” of the invention and the specification includespolyethylene naphthalate having a structure including one or more kindsof other components (for example, copolymerization component, andcomponent introduced to a terminal or a side chain), in addition to thecomponent described above.

In addition, in the one embodiment, the non-magnetic support of themagnetic tape can be an aromatic polyamide support. In the invention andthe specification, the “aromatic polyamide” means a resin containing anaromatic skeleton and a plurality of amide bonds. An aromatic ringincluded in an aromatic skeleton including the aromatic polyamide is notparticularly limited. Specific examples of the aromatic ring include abenzene ring and the like. The “aromatic polyamide support” means asupport including at least one layer of an aromatic polyamide film. The“aromatic polyamide film” refers to a film in which the largestcomponent in the component configuring this film based on mass isaromatic polyamide. The “aromatic polyamide support” of the inventionand the specification include a support in which all of resin filmsincluded in this support is the aromatic polyamide film and a supportincluding the aromatic polyamide film and the other resin film. Specificexamples of the aromatic polyamide support include a single aromaticpolyamide film, a laminated film of two or more layers of the aromaticpolyamide film having the same constituting component, a laminated filmof two or more layers of the aromatic polyamide film having differentconstituting components, and a laminated film including one or morelayers of the aromatic polyamide film and one or more layers of resinfilm other than the aromatic polyamide. In the laminated film, anadhesive layer or the like may be randomly included between two adjacentlayers. In addition, the aromatic polyamide support may randomly includea metal film and/or a metal oxide film formed by performing vapordeposition or the like on one or both surfaces.

In addition, the non-magnetic support can be a biaxial stretching film,and may be a film subjected to corona discharge, plasma treatment, easyadhesion treatment, heat treatment, or the like.

As an indicator of physical properties of the non-magnetic support, forexample, a moisture content can be used. In the invention and thespecification, the moisture content of the non-magnetic support is avalue obtained by the following method. The moisture content shown inthe table which will be described later is a value obtained by thefollowing method.

A test piece (for example, a test piece having a mass of several grams)cut out from the non-magnetic support, moisture content of which is tobe measured, is dried in a vacuum dryer at a temperature of 180° C. andunder a pressure of 100 Pa (pascal) or less until a constant weight isobtained. The mass of the dried test piece is defined as W1. W1 is avalue measured in a measurement environment of a temperature of 23° C.and relative humidity of 50% within 30 seconds after being taken out ofthe vacuum dryer. Next, the mass of this test piece after being placedin an environment of a temperature of 25° C. and relative humidity of75% for 48 hours is defined as W2. W2 is a value measured in ameasurement environment of a temperature of 23° C. and relative humidityof 50% within 30 seconds after being taken out of the environment. Themoisture content is calculated by the following equation.

Moisture content (%)=[(W2−W1)/W1]×100

For example, it is also possible to obtain the moisture content of thenon-magnetic support by the method described above, after removingportions other than the non-magnetic support such as the magnetic layerfrom the magnetic tape by a well-known method (for example, film removalusing an organic solvent).

In one embodiment, the moisture content of the non-magnetic support ofthe magnetic tape is preferably 2.0% or less, more preferably 1.8% orless, even more preferably 1.6% or less, further preferably 1.4% orless, even further preferably 1.2% or less, and still preferably 1.0% orless. In addition, the moisture content of the non-magnetic support ofthe magnetic tape can be 0%, 0% or more, more than 0%, or 0.1% or more.The use of the non-magnetic support having a low moisture content cancontribute to an increase in value of the medium life. This is mainlybecause it is considered that the use of the non-magnetic support havinga low moisture content contributes to a decrease in value of “B”obtained by the method described above.

As an indicator of physical properties of the non-magnetic support, aYoung's modulus can also be used. The Young's modulus of thenon-magnetic support in the present invention and the presentspecification is a value measured by the following method in ameasurement environment of a temperature of 23° C. and a relativehumidity of 50%. The Young's modulus shown in the following table is avalue obtained by the following method using TENSILON manufactured byBaldwin Corporation as a universal tensile testing device.

A test piece cut out from the non-magnetic support to be measured ispulled by a universal tensile testing device under the conditions of achuck-to-chuck distance of 100 mm, a tensile rate of 10 mm/min, and achart rate of 500 mm/min. As the universal tensile testing device, forexample, a commercially available universal tensile testing device suchas TENSILON manufactured by Baldwin Corporation or a universal tensiletesting device having a well-known configuration can be used. TheYoung's moduli of the test piece in the longitudinal direction and thewidth direction are respectively calculated from a tangent line of arising portion of a load-elongation curve obtained as described above.Here, the longitudinal direction and the width direction of the testpiece mean a longitudinal direction and a width direction in a casewhere this test piece is included in the magnetic tape.

For example, it is also possible to obtain the Young's moduli of thenon-magnetic support in the longitudinal direction and the widthdirection can be obtained by the method described above, after removingportions other than the non-magnetic support such as the magnetic layerfrom the magnetic tape by a well-known method (for example, film removalusing an organic solvent).

In one embodiment, the Young's modulus in the longitudinal direction ofthe non-magnetic support of the magnetic tape is preferably 3000 MPa ormore, more preferably 4000 MPa or more, even more preferably 5000 MPa ormore, and further preferably 6000 MPa or more. In addition, the Young'smodulus of the non-magnetic support of the magnetic tape in thelongitudinal direction can be 15000 MPa or less, 13000 MPa or less, or12000 MPa or less. In the width direction, the Young's modulus in thewidth direction of the non-magnetic support of the magnetic tape ispreferably 2000 MPa or more, more preferably 3000 MPa or more, even morepreferably 4000 MPa or more, and further preferably 5000 MPa or more. Inaddition, the Young's modulus of the non-magnetic support of themagnetic tape in the width direction can be 12000 MPa or less, 11000 MPaor less, or 10000 MPa or less. During manufacturing the magnetic tape,for the non-magnetic support, usually, a machine direction (MDdirection) of a film is used as the longitudinal direction and atransverse direction (TD direction) is used as the width direction. Inaddition, in one embodiment, the Young's modulus in the longitudinaldirection is preferably greater than the Young's modulus in the widthdirection, and a difference (Young's modulus in the longitudinaldirection—Young's modulus in the width direction) is more preferably inthe range of 800 to 3000 MPa. The medium life can also be controlled byYoung's modulus of the non-magnetic support.

The moisture content and the Young's modulus of the non-magnetic supportcan be controlled by a type and a mixing ratio of the componentsconstituting the support, manufacturing conditions of the support, andthe like. For example, in a biaxial stretching process, the Young'smodulus in the longitudinal direction and the Young's modulus in thewidth direction can be controlled respectively by adjusting thestretching ratio in each direction.

Magnetic Layer Ferromagnetic Powder

As the ferromagnetic powder included in the magnetic layer of themagnetic tape, a well-known ferromagnetic powder can be used as one kindor in combination of two or more kinds as the ferromagnetic powder usedin the magnetic layer of various magnetic recording media. It ispreferable to use a ferromagnetic powder having a small average particlesize as the ferromagnetic powder, from a viewpoint of improvement of arecording density. From this viewpoint, an average particle size of theferromagnetic powder is preferably equal to or smaller than 50 nm, morepreferably equal to or smaller than 45 nm, even more preferably equal toor smaller than 40 nm, further preferably equal to or smaller than 35nm, further more preferably equal to or smaller than 30 nm, further evenmore preferably equal to or smaller than 25 nm, and still preferablyequal to or smaller than 20 nm. Meanwhile, from a viewpoint of stabilityof magnetization, the average particle size of the ferromagnetic powderis preferably equal to or greater than 5 nm, more preferably equal to orgreater than 8 nm, even more preferably equal to or greater than 10 nm,still preferably equal to or greater than 15 nm, and still morepreferably equal to or greater than 20 nm.

Hexagonal Ferrite Powder

As a preferred specific example of the ferromagnetic powder, a hexagonalferrite powder can be used. For details of the hexagonal ferrite powder,descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A,paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 ofJP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can bereferred to, for example.

In the invention and the specification, the “hexagonal ferrite powder”is a ferromagnetic powder in which a hexagonal ferrite type crystalstructure is detected as a main phase by X-ray diffraction analysis. Themain phase is a structure to which a diffraction peak at the highestintensity in an X-ray diffraction spectrum obtained by the X-raydiffraction analysis belongs. For example, in a case where thediffraction peak at the highest intensity in the X-ray diffractionspectrum obtained by the X-ray diffraction analysis belongs to ahexagonal ferrite type crystal structure, it is determined that thehexagonal ferrite type crystal structure is detected as a main phase. Ina case where only a single structure is detected by the X-raydiffraction analysis, this detected structure is set as a main phase.The hexagonal ferrite type crystal structure includes at least an ironatom, a divalent metal atom, and an oxygen atom as constituting atoms. Adivalent metal atom is a metal atom which can be divalent cations asions, and examples thereof include an alkali earth metal atom such as astrontium atom, a barium atom, or a calcium atom, and a lead atom. Inthe invention and the specification, the hexagonal strontium ferritepowder is powder in which a main divalent metal atom included in thispowder is a strontium atom, and the hexagonal barium ferrite powder is apowder in which a main divalent metal atom included in this powder is abarium atom. The main divalent metal atom is a divalent metal atomoccupying the greatest content in the divalent metal atom included inthe powder based on atom %. However, the divalent metal atom describedabove does not include rare earth atom. The “rare earth atom” of theinvention and the specification is selected from the group consisting ofa scandium atom (Sc), a yttrium atom (Y), and a lanthanoid atom. Thelanthanoid atom is selected from the group consisting of a lanthanumatom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymiumatom (Nd), a promethium atom (Pm), a samarium atom (Sm), an europiumatom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosiumatom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom(Tm), a ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is oneembodiment of the hexagonal ferrite powder will be described morespecifically.

An activation volume of the hexagonal strontium ferrite powder ispreferably in a range of 800 to 1,600 nm³. The atomized hexagonalstrontium ferrite powder showing the activation volume in the rangedescribed above is suitable for manufacturing a magnetic tape exhibitingexcellent electromagnetic conversion characteristics. The activationvolume of the hexagonal strontium ferrite powder is preferably equal toor greater than 800 nm³, and can also be, for example, equal to orgreater than 850 nm³. In addition, from a viewpoint of further improvingthe electromagnetic conversion characteristics, the activation volume ofthe hexagonal strontium ferrite powder is more preferably equal to orsmaller than 1,500 nm³, even more preferably equal to or smaller than1,400 nm³, still preferably equal to or smaller than 1,300 nm³, stillmore preferably equal to or smaller than 1,200 nm³, and still even morepreferably equal to or smaller than 1,100 nm³. The same applies to theactivation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and anindicator showing a magnetic magnitude of the particles. Regarding theactivation volume and an anisotropy constant Ku which will be describedlater disclosed in the invention and the specification, magnetic fieldsweep rates of a coercivity Hc measurement part at time points of 3minutes and 30 minutes are measured by using an oscillation sample typemagnetic-flux meter (measurement temperature: 23° C.±1° C.), and theactivation volume and the anisotropy constant Ku are values acquiredfrom the following relational expression of Hc and an activation volumeV. A unit of the anisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³.

Hc=2Ku/Ms{1−[RkT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturationmagnetization (unit: kA/m), k: Boltzmann's constant, T: absolutetemperature (unit: K), V: activation volume (unit: cm³), A: spinprecession frequency (unit: s⁻¹), and t: magnetic field reversal time(unit: s)]

The anisotropy constant Ku can be used as an indicator of reduction ofthermal fluctuation, that is, improvement of thermal stability. Thehexagonal strontium ferrite powder can preferably have Ku equal to orgreater than 1.8×10⁵ J/m³, and more preferably have Ku equal to orgreater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontiumferrite powder can be, for example, equal to or smaller than 2.5×10⁵J/m³. However, the high Ku is preferable, because it means high thermalstability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include the rareearth atom. In a case where the hexagonal strontium ferrite powderincludes the rare earth atom, a content (bulk content) of the rare earthatom is preferably 0.5 to 5.0 atom % with respect to 100 atom % of theiron atom. In the one embodiment, the hexagonal strontium ferrite powderincluding the rare earth atom can have a rare earth atom surface layerportion uneven distribution. The “rare earth atom surface layer portionuneven distribution” of the invention and the specification means that acontent of rare earth atom with respect to 100 atom % of iron atom in asolution obtained by partially dissolving the hexagonal strontiumferrite powder with acid (hereinafter, referred to as a “rare earth atomsurface layer portion content” or simply a “surface layer portioncontent” regarding the rare earth atom) and a content of rare earth atomwith respect to 100 atom % of iron atom in a solution obtained bytotally dissolving the hexagonal strontium ferrite powder with acid(hereinafter, referred to as a “rare earth atom bulk content” or simplya “bulk content” regarding the rare earth atom)

satisfy a ratio of rare earth atom surface layer portion content/rareearth atom bulk content>1.0. The content of rare earth atom of thehexagonal strontium ferrite powder which will be described later isidentical to the rare earth atom bulk content. With respect to this, thepartial dissolving using acid is to dissolve the surface layer portionof particles configuring the hexagonal strontium ferrite powder, andaccordingly, the content of rare earth atom in the solution obtained bythe partial dissolving is the content of rare earth atom in the surfacelayer portion of the particles configuring the hexagonal strontiumferrite powder. The rare earth atom surface layer portion contentsatisfying a ratio of “rare earth atom surface layer portioncontent/rare earth atom bulk content>1.0” means that the rare earthatoms are unevenly distributed in the surface layer portion (that is, alarger amount of the rare earth atoms is present, compared to thatinside), among the particles configuring the hexagonal strontium ferritepowder. The surface layer portion of the invention and the specificationmeans a part of the region of the particles configuring the hexagonalstrontium ferrite powder towards the inside from the surface.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, a content (bulk content) of the rare earth atom ispreferably 0.5 to 5.0 atom % with respect to 100 atom % of the ironatom. It is considered that the rare earth atom having the bulk contentin the range described above and uneven distribution of the rare earthatom in the surface layer portion of the particles configuring thehexagonal strontium ferrite powder contribute to the prevention of adecrease in reproducing output during the repeated reproducing. It issurmised that this is because the rare earth atom having the bulkcontent in the range described above included in the hexagonal strontiumferrite powder and the uneven distribution of the rare earth atom in thesurface layer portion of the particles configuring the hexagonalstrontium ferrite powder can increase the anisotropy constant Ku. As thevalue of the anisotropy constant Ku is high, occurrence of a phenomenoncalled thermal fluctuation (that is, improvement of thermal stability)can be prevented. By preventing the occurrence of the thermalfluctuation, a decrease in reproducing output during the repeatedreproducing can be prevented. It is surmised that the unevendistribution of the rare earth atom in the surface layer portion of theparticles of the hexagonal strontium ferrite powder contributes tostabilization of a spin at an iron (Fe) site in a crystal lattice of thesurface layer portion, thereby increasing the anisotropy constant Ku.

In addition, it is surmised that the use of the hexagonal strontiumferrite powder having the rare earth atom surface layer portion unevendistribution as the ferromagnetic powder of the magnetic layer alsocontributes to the prevention of chipping of the surface of the magneticlayer due to the sliding with the magnetic head. That is, it is surmisedthat, the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution can also contribute to theimprovement of running durability of the magnetic tape. It is surmisedthat this is because the uneven distribution of the rare earth atom onthe surface of the particles configuring the hexagonal strontium ferritepowder contributes to improvement of an interaction between the surfaceof the particles and an organic substance (for example, binding agentand/or additive) included in the magnetic layer, thereby improvingstrength of the magnetic layer.

From a viewpoint of even more preventing reduction of the reproductionoutput in the repeated reproduction and/or a viewpoint of furtherimproving running durability, the content of rare earth atom (bulkcontent) is more preferably in a range of 0.5 to 4.5 atom %, even morepreferably in a range of 1.0 to 4.5 atom %, and still preferably in arange of 1.5 to 4.5 atom %.

The bulk content is a content obtained by totally dissolving thehexagonal strontium ferrite powder. In the invention and thespecification, the content of the atom is a bulk content obtained bytotally dissolving the hexagonal strontium ferrite powder, unlessotherwise noted. The hexagonal strontium ferrite powder including therare earth atom may include only one kind of rare earth atom or mayinclude two or more kinds of rare earth atom, as the rare earth atom. Ina case where two or more kinds of rare earth atom are included, the bulkcontent is obtained from the total of the two or more kinds of rareearth atoms. The same also applies to the other components of theinvention and the specification. That is, for a given component, onlyone kind may be used or two or more kinds may be used, unless otherwisenoted. In a case where two or more kinds are used, the content is acontent of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, the rare earth atom included therein may be any one or morekinds of the rare earth atom. Examples of the rare earth atom preferablefrom a viewpoint of even more suppressing reduction of the reproductionoutput during the repeated reproduction can include a neodymium atom, asamarium atom, a yttrium atom, and a dysprosium atom, a neodymium atom,a samarium atom, and a yttrium atom are more preferable, and a neodymiumatom is even more preferable.

In the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution, a degree of unevendistribution of the rare earth atom is not limited, as long as the rareearth atom is unevenly distributed in the surface layer portion of theparticles configuring the hexagonal strontium ferrite powder. Forexample, regarding the hexagonal strontium ferrite powder having therare earth atom surface layer portion uneven distribution, a ratio ofthe surface layer portion content of the rare earth atom obtained bypartial dissolving performed under the dissolving conditions which willbe described later and the bulk content of the rare earth atom obtainedby total dissolving performed under the dissolving conditions which willbe described later, “surface layer portion content/bulk content” isgreater than 1.0 and can be equal to or greater than 1.5. The “surfacelayer portion content/bulk content” greater than 1.0 means that the rareearth atoms are unevenly distributed in the surface layer portion (thatis, a larger amount of the rare earth atoms is present, compared to thatinside), in the particles configuring the hexagonal strontium ferritepowder. A ratio of the surface layer portion content of the rare earthatom obtained by partial dissolving performed under the dissolvingconditions which will be described later and the bulk content of therare earth atom obtained by total dissolving performed under thedissolving conditions which will be described later, “surface layerportion content/bulk content” can be, for example, equal to or smallerthan 10.0, equal to or smaller than 9.0, equal to or smaller than 8.0,equal to or smaller than 7.0, equal to or smaller than 6.0, equal to orsmaller than 5.0, or equal to or smaller than 4.0. However, in thehexagonal strontium ferrite powder having the rare earth atom surfacelayer portion uneven distribution, the “surface layer portioncontent/bulk content” is not limited to the exemplified upper limit orthe lower limit, as long as the rare earth atom is unevenly distributedin the surface layer portion of the particles configuring the hexagonalstrontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonalstrontium ferrite powder will be described below. Regarding thehexagonal strontium ferrite powder present as the powder, sample powderfor the partial dissolving and the total dissolving are collected frompowder of the same batch. Meanwhile, regarding the hexagonal strontiumferrite powder included in a magnetic layer of a magnetic tape, a partof the hexagonal strontium ferrite powder extracted from the magneticlayer is subjected to the partial dissolving and the other part issubjected to the total dissolving. The extraction of the hexagonalstrontium ferrite powder from the magnetic layer can be performed by,for example, a method disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonalstrontium ferrite powder remaining in the solution can be visuallyconfirmed in a case of the completion of the dissolving. For example, byperforming the partial dissolving, a region of the particles configuringthe hexagonal strontium ferrite powder which is 10% to 20% by mass withrespect to 100% by mass of a total of the particles can be dissolved. Onthe other hand, the total dissolving means dissolving performed untilthe hexagonal strontium ferrite powder remaining in the solution is notvisually confirmed in a case of the completion of the dissolving.

The partial dissolving and the measurement of the surface layer portioncontent are, for example, performed by the following method. However,dissolving conditions such as the amount of sample powder and the likedescribed below are merely examples, and dissolving conditions capableof performing the partial dissolving and the total dissolving can berandomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 1 mol/L is held on ahot plate at a set temperature of 70° C. for 1 hour. The obtainedsolution is filtered with a membrane filter having a hole diameter of0.1 The element analysis of the filtrate obtained as described above isperformed by an inductively coupled plasma (ICP) analysis device. Bydoing so, the surface layer portion content of the rare earth atom withrespect to 100 atom % of the iron atom can be obtained. In a case wherea plurality of kinds of rare earth atoms are detected from the elementanalysis, a total content of the entirety of the rare earth atoms is thesurface layer portion content. The same applies to the measurement ofthe bulk content.

Meanwhile, the total dissolving and the measurement of the bulk contentare, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 4 mol/L is held on ahot plate at a set temperature of 80° C. for 3 hours. After that, theprocess is performed in the same manner as in the partial dissolving andthe measurement of the surface layer portion content, and the bulkcontent with respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regards to this point, in hexagonal strontium ferritepowder which includes the rare earth atom but does not have the rareearth atom surface layer portion uneven distribution, as tends tosignificantly decrease, compared to that in hexagonal strontium ferritepowder not including the rare earth atom. With respect to this, it isthought that, hexagonal strontium ferrite powder having the rare earthatom surface layer portion uneven distribution is also preferable forpreventing such a significant decrease in as. In one embodiment, as ofthe hexagonal strontium ferrite powder can be equal to or greater than45 A×m²/kg and can also be equal to or greater than 47 A×m²/kg. On theother hand, from a viewpoint of noise reduction, as is preferably equalto or smaller than 80 A×m²/kg and more preferably equal to or smallerthan 60 A×m²/kg. as can be measured by using a well-known measurementdevice capable of measuring magnetic properties such as an oscillationsample type magnetic-flux meter. In the invention and the specification,the mass magnetization σs is a value measured at a magnetic fieldstrength of 15 kOe, unless otherwise noted. 1 [kOe]=(10⁶/4π) [A/m]

Regarding the content (bulk content) of the constituting atom in thehexagonal strontium ferrite powder, a content of the strontium atom canbe, for example, 2.0 to 15.0 atom % with respect to 100 atom % of theiron atom. In one embodiment, in the hexagonal strontium ferrite powder,the divalent metal atom included in this powder can be only a strontiumatom. In another embodiment, the hexagonal strontium ferrite powder canalso include one or more kinds of other divalent metal atoms, inaddition to the strontium atom. For example, the hexagonal strontiumferrite powder can include a barium atom and/or a calcium atom. In acase where the other divalent metal atom other than the strontium atomis included, a content of a barium atom and a content of a calcium atomin the hexagonal strontium ferrite powder respectively can be, forexample, 0.05 to 5.0 atom % with respect to 100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbitetype (also referred to as an “M type”), a W type, a Y type, and a Z typeare known. The hexagonal strontium ferrite powder may have any crystalstructure. The crystal structure can be confirmed by X-ray diffractionanalysis. In the hexagonal strontium ferrite powder, a single crystalstructure or two or more kinds of crystal structure can be detected bythe X-ray diffraction analysis. For example, in one embodiment, in thehexagonal strontium ferrite powder, only the M type crystal structurecan be detected by the X-ray diffraction analysis. For example, the Mtype hexagonal ferrite is represented by a compositional formula ofAFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where thehexagonal strontium ferrite powder has the M type, A is only a strontiumatom (Sr), or in a case where a plurality of divalent metal atoms areincluded as A, the strontium atom (Sr) occupies the hexagonal strontiumferrite powder with the greatest content based on atom % as describedabove. A content of the divalent metal atom in the hexagonal strontiumferrite powder is generally determined according to the type of thecrystal structure of the hexagonal ferrite and is not particularlylimited. The same applies to a content of an iron atom and a content ofan oxygen atom. The hexagonal strontium ferrite powder at least includesan iron atom, a strontium atom, and an oxygen atom, and can also includea rare earth atom. In addition, the hexagonal strontium ferrite powdermay or may not include atoms other than these atoms. As an example, thehexagonal strontium ferrite powder may include an aluminum atom (Al). Acontent of the aluminum atom can be, for example, 0.5 to 10.0 atom %with respect to 100 atom % of the iron atom. From a viewpoint of evenmore preventing the reduction of the reproduction output during therepeated reproduction, the hexagonal strontium ferrite powder includesthe iron atom, the strontium atom, the oxygen atom, and the rare earthatom, and a content of the atoms other than these atoms is preferablyequal to or smaller than 10.0 atom %, more preferably 0 to 5.0 atom %,and may be 0 atom % with respect to 100 atom % of the iron atom. Thatis, in one embodiment, the hexagonal strontium ferrite powder may notinclude atoms other than the iron atom, the strontium atom, the oxygenatom, and the rare earth atom. The content shown with atom % describedabove is obtained by converting the content (unit: % by mass) of eachatom obtained by totally dissolving the hexagonal strontium ferritepowder into a value shown as atom % by using the atomic weight of eachatom. In addition, in the invention and the specification, a given atomwhich is “not included” means that the content thereof obtained byperforming total dissolving and measurement by using an ICP analysisdevice is 0% by mass. A detection limit of the ICP analysis device isgenerally equal to or smaller than 0.01 ppm (parts per million) based onmass. The expression “not included” is used as a meaning including thata given atom is included with the amount smaller than the detectionlimit of the ICP analysis device. In one embodiment, the hexagonalstrontium ferrite powder does not include a bismuth atom (Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder, aferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, an ε-ironoxide powder can also be used. In the invention and the specification,the “ε-iron oxide powder” is a ferromagnetic powder in which an ε-ironoxide type crystal structure is detected as a main phase by X-raydiffraction analysis. For example, in a case where the diffraction peakat the highest intensity in the X-ray diffraction spectrum obtained bythe X-ray diffraction analysis belongs to an ε-iron oxide type crystalstructure, it is determined that the ε-iron oxide type crystal structureis detected as a main phase. As a manufacturing method of the ε-ironoxide powder, a manufacturing method from a goethite, a reverse micellemethod, and the like are known. All of the manufacturing methods arewell known. For the method of manufacturing the ε-iron oxide powder inwhich a part of Fe is substituted with substitutional atoms such as Ga,Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. PowderMetallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mater. Chem. C,2013, 1, pp.5200-5206 can be referred, for example. However, themanufacturing method of the ε-iron oxide powder capable of being used asthe ferromagnetic powder in the magnetic layer of the magnetic tape isnot limited to the method described here.

An activation volume of the ε-iron oxide powder is preferably 300 to1,500 nm³. The atomized ε-iron oxide powder showing the activationvolume in the range described above is suitable for manufacturing amagnetic tape exhibiting excellent electromagnetic conversioncharacteristics. The activation volume of the s-iron oxide powder ispreferably equal to or greater than 300 nm³, and can also be, forexample, equal to or greater than 500 nm³. In addition, from a viewpointof further improving the electromagnetic conversion characteristics, theactivation volume of the ε-iron oxide powder is more preferably equal toor smaller than 1,400 nm³, even more preferably equal to or smaller than1,300 nm³, still preferably equal to or smaller than 1,200 nm³, andstill more preferably equal to or smaller than 1,100 nm³.

The anisotropy constant Ku can be used as an indicator of reduction ofthermal fluctuation, that is, improvement of thermal stability. Theε-iron oxide powder can preferably have Ku equal to or greater than3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, forexample, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku ispreferable, because it means high thermal stability, and thus, Ku is notlimited to the exemplified value.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regard to this point, in one embodiment, as of theε-iron oxide powder can be equal to or greater than 8 A×m²/kg and canalso be equal to or greater than 12 A×m²/kg. On the other hand, from aviewpoint of noise reduction, σs of the ε-iron oxide powder ispreferably equal to or smaller than 40 A×m²/kg and more preferably equalto or smaller than 35 A×m²/kg.

In the invention and the specification, average particle sizes ofvarious powders such as the ferromagnetic powder and the like are valuesmeasured by the following method with a transmission electronmicroscope, unless otherwise noted.

The powder is imaged at an imaging magnification ratio of 100,000 with atransmission electron microscope, the image is printed onto aphotographic printing paper so that a total magnification ratio of500,000 of an image of particles configuring the powder is obtained. Atarget particle is selected from the obtained image of particles, anoutline of the particle is traced with a digitizer, and a size of theparticle (primary particle) is measured. The primary particle is anindependent particle which is not aggregated.

The measurement described above is performed regarding 500 particlesrandomly extracted. An arithmetic mean of the particle size of 500particles obtained as described above is the average particle size ofthe powder. As the transmission electron microscope, a transmissionelectron microscope H-9000 manufactured by Hitachi, Ltd. can be used,for example. In addition, the measurement of the particle size can beperformed by a well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the invention and thespecification, the powder means an aggregate of a plurality ofparticles. For example, the ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. The aggregate of the plurality ofparticles not only includes an embodiment in which particles configuringthe aggregate are directly in contact with each other, but also includesan embodiment in which a binding agent or an additive which will bedescribed later is interposed between the particles. A term, particlesmay be used for representing the powder.

As a method for collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted, (1) in acase where the shape of the particle observed in the particle imagedescribed above is a needle shape, a fusiform shape, or a columnar shape(here, a height is greater than a maximum long diameter of a bottomsurface), the size (particle size) of the particles configuring thepowder is shown as a length of a major axis configuring the particle,that is, a major axis length, (2) in a case where the shape of theparticle is a planar shape or a columnar shape (here, a thickness or aheight is smaller than a maximum long diameter of a plate surface or abottom surface), the particle size is shown as a maximum long diameterof the plate surface or the bottom surface, and (3) in a case where theshape of the particle is a sphere shape, a polyhedron shape, or anunspecified shape, and the major axis configuring the particles cannotbe specified from the shape, the particle size is shown as an equivalentcircle diameter. The equivalent circle diameter is a value obtained by acircle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a minor axis, that is, a minor axis length of the particles ismeasured in the measurement described above, a value of (major axislength/minor axis length) of each particle is obtained, and anarithmetic mean of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the minoraxis length as the definition of the particle size is a length of aminor axis configuring the particle, in a case of (2), the minor axislength is a thickness or a height, and in a case of (3), the major axisand the minor axis are not distinguished, thus, the value of (major axislength/minor axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average major axislength, and in a case of the same definition (2), the average particlesize is an average plate diameter. In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably 50% to 90% by mass and more preferably 60%to 90% by mass with respect to a total mass of the magnetic layer. Ahigh filling percentage of the ferromagnetic powder in the magneticlayer is preferable from a viewpoint of improvement of recordingdensity.

Binding Agent

The magnetic tape may be a coating type magnetic tape, and can include abinding agent in the magnetic layer. The binding agent is one or morekinds of resin. As the binding agent, various resins normally used as abinding agent of a coating type magnetic tape can be used. As thebinding agent, a resin selected from a polyurethane resin, a polyesterresin, a polyamide resin, a vinyl chloride resin, an acrylic resinobtained by copolymerizing styrene, acrylonitrile, or methylmethacrylate, a cellulose resin such as nitrocellulose, an epoxy resin,a phenoxy resin, and a polyvinylalkylal resin such as polyvinyl acetalor polyvinyl butyral can be used alone or a plurality of resins can bemixed with each other to be used. Among these, a polyurethane resin, anacrylic resin, a cellulose resin, and a vinyl chloride resin arepreferable. These resins may be a homopolymer or a copolymer. Theseresins can be used as the binding agent even in the non-magnetic layerand/or a back coating layer which will be described later.

For the binding agent described above, descriptions disclosed inparagraphs 0028 to 0031 of JP2010-24113A can be referred to. An averagemolecular weight of the resin used as the binding agent can be, forexample, 10,000 to 200,000 as a weight-average molecular weight. Theweight-average molecular weight of the invention and the specificationis a value obtained by performing polystyrene conversion of a valuemeasured by gel permeation chromatography (GPC) under the followingmeasurement conditions. The weight-average molecular weight of thebinding agent shown in examples which will be described later is a valueobtained by performing polystyrene conversion of a value measured underthe following measurement conditions. The amount of the binding agentused can be, for example, 1.0 to 30.0 parts by mass with respect to100.0 parts by mass of the ferromagnetic powder.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mmID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

Curing Agent

A curing agent can also be used together with the resin which can beused as the binding agent. As the curing agent, in one embodiment, athermosetting compound which is a compound in which a curing reaction(crosslinking reaction) proceeds due to heating can be used, and inanother embodiment, a photocurable compound in which a curing reaction(crosslinking reaction) proceeds due to light irradiation can be used.At least a part of the curing agent is included in the magnetic layer ina state of being reacted (crosslinked) with other components such as thebinding agent, by proceeding the curing reaction in the magnetic layerforming step. This point is the same as regarding a layer formed byusing a composition, in a case where the composition used for formingthe other layer includes the curing agent. The preferred curing agent isa thermosetting compound, and polyisocyanate is suitable. For thedetails of polyisocyanate, descriptions disclosed in paragraphs 0124 and0125 of JP2011-216149A can be referred to. The amount of the curingagent can be, for example, 0 to 80.0 parts by mass with respect to 100.0parts by mass of the binding agent in the magnetic layer formingcomposition, and is preferably 50.0 to 80.0 parts by mass, from aviewpoint of improvement of hardness of the magnetic layer.

Additives

The magnetic layer may include one or more kinds of additives, asnecessary. As the additives, a commercially available product can besuitably selected and used according to the desired properties.Alternatively, a compound synthesized by a well-known method can be usedas the additives. The additive can be used with a random amount. As theadditives, the curing agent described above is used as an example. Inaddition, examples of the additive included in the magnetic layerinclude a non-magnetic powder (for example, inorganic powder, carbonblack, or the like), a lubricant, a dispersing agent, a dispersingassistant, a fungicide, an antistatic agent, and an antioxidant. For thelubricant, a description disclosed in paragraphs 0030 to 0033, 0035, and0036 of JP2016-126817A can be referred to. The lubricant may be includedin the non-magnetic layer which will be described later. For thelubricant which may be included in the non-magnetic layer, a descriptiondisclosed in paragraphs 0030, 0031, 0034, 0035, and 0036 ofJP2016-126817A can be referred to. For the dispersing agent, adescription disclosed in paragraphs 0061 and 0071 of JP2012-133837A canbe referred to. The dispersing agent may be added to a non-magneticlayer forming composition. For the dispersing agent which can be addedto the non-magnetic layer forming composition, a description disclosedin paragraph 0061 of JP2012-133837A can be referred to. As thenon-magnetic powder which may be included in the magnetic layer,non-magnetic powder which can function as an abrasive, non-magneticpowder (for example, non-magnetic colloid particles) which can functionas a projection formation agent which forms projections suitablyprotruded from the surface of the magnetic layer, and the like can beused. For example, for the abrasive, a description disclosed inparagraphs 0030 to 0032 of JP2004-273070A can be referred to. As theprojection formation agent, colloidal particles are preferable, and froma viewpoint of availability, inorganic colloidal particles arepreferable, inorganic oxide colloidal particles are more preferable, andsilica colloidal particles (colloidal silica) are even more preferable.Average particle sizes of the abrasive and the projection formationagent are respectively preferably 30 to 200 nm and more preferably 50 to100 nm.

The magnetic layer described above can be provided on the surface of thenon-magnetic support directly or indirectly through the non-magneticlayer.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on the surface of the non-magneticsupport or may include a magnetic layer on the surface of thenon-magnetic support through the non-magnetic layer including thenon-magnetic powder. The non-magnetic powder used in the non-magneticlayer may be a powder of an inorganic substance or a powder of anorganic substance. In addition, carbon black and the like can be used.Examples of powder of the inorganic substance include powder of metal,metal oxide, metal carbonate, metal sulfate, metal nitride, metalcarbide, and metal sulfide. The non-magnetic powder can be purchased asa commercially available product or can be manufactured by a well-knownmethod. For details thereof, descriptions disclosed in paragraphs 0146to 0150 of JP2011-216149A can be referred to. For carbon black which canbe used in the non-magnetic layer, descriptions disclosed in paragraphs0040 and 0041 of JP2010-24113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably 50% to 90% by mass and more preferably 60% to 90% by masswith respect to a total mass of the non-magnetic layer.

The non-magnetic layer can include a binding agent and can also includeadditives. In regards to other details of a binding agent and additivesof the non-magnetic layer, the well-known technology regarding thenon-magnetic layer can be applied. In addition, in regards to the typeand the content of the binding agent, and the type and the content ofthe additive, for example, the well-known technology regarding themagnetic layer can be applied.

The non-magnetic layer of the invention and the specification alsoincludes a substantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Back Coating Layer

The magnetic tape may or may not include a back coating layer includinga non-magnetic powder on a surface side of the non-magnetic supportopposite to the surface side provided with the magnetic layer. The backcoating layer preferably includes any one or both of carbon black andinorganic powder. The back coating layer can include a binding agent andcan also include additives. In regards to the binding agent included inthe back coating layer and additives, a well-known technology regardingthe back coating layer can be applied, and a well-known technologyregarding the list of the magnetic layer and/or the non-magnetic layercan also be applied. For example, for the back coating layer,descriptions disclosed in paragraphs 0018 to 0020 of JP2006-331625A andpage 4, line 65, to page 5, line 38, of US7029774B can be referred to.

Various Thicknesses

Regarding a thickness (total thickness) of the magnetic tape, it hasbeen required to increase recording capacity (increase in capacity) ofthe magnetic tape along with the enormous increase in informationcontent in recent years. As a unit for increasing the capacity, athickness of the magnetic tape is reduced (hereinafter, also referred toas “thinning”) and a length of the magnetic tape accommodated in onereel of the magnetic tape cartridge is increased. From this point, thethickness (total thickness) of the magnetic tape is preferably 5.6 μm orless, more preferably 5.5 μm or less, even more preferably 5.4 μm orless, and still preferably 5.3 μm or less. In addition, from a viewpointof ease of handling, the thickness of the magnetic tape is preferably3.0 μm or more and more preferably 3.5 μm or more.

The thickness (total thickness) of the magnetic tape can be measured bythe following method.

Ten tape samples (for example, length of 5 to 10 cm) are cut out from arandom portion of the magnetic tape, these tape samples are stacked, andthe thickness is measured. A value which is one tenth of the measuredthickness (thickness per tape sample) is set as the tape thickness. Thethickness measurement can be performed using a well-known measurementdevice capable of performing the thickness measurement at 0.1 μm order.

A thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

A thickness of the magnetic layer can be optimized according to asaturation magnetization amount of a magnetic head used, a head gaplength, a recording signal band, and the like, is normally 0.01 μm to0.15 μm, and is preferably 0.02 μm to 0.12 μm and more preferably 0.03μm to 0.1 μm, from a viewpoint of realization of high-density recording.The magnetic layer may be at least single layer, the magnetic layer maybe separated into two or more layers having different magneticproperties, and a configuration of a well-known multilayered magneticlayer can be applied. A thickness of the magnetic layer in a case wherethe magnetic layer is separated into two or more layers is the totalthickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably 0.9 μm or less andmore preferably 0.1 to 0.7 μm.

Various thicknesses such as the thickness of the magnetic layer and thelike can be obtained by the following method.

A cross section of the magnetic tape in the thickness direction isexposed with an ion beam and the cross section observation of theexposed cross section is performed using a scanning electron microscope.Various thicknesses can be obtained as the arithmetic mean of thethicknesses obtained at two random portions in the cross sectionobservation. Alternatively, various thicknesses can be obtained as adesigned thickness calculated under the manufacturing conditions.

Manufacturing Step Preparation of Each Layer Forming Composition

A composition for forming the magnetic layer, the non-magnetic layer, orthe back coating layer generally includes a solvent, together with thevarious components described above. As the solvent, one kind or two ormore kinds of various kinds of solvents usually used for producing acoating type magnetic recording medium can be used. The content of thesolvent in each layer forming composition is not particularly limited.For the solvent, a description disclosed in a paragraph 0153 ofJP2011-216149A can be referred to. A concentration of solid content anda solvent composition in each layer forming composition may be suitablyadjusted according to handleability of the composition, coatingconditions, and a thickness of each layer to be formed. A step ofpreparing a composition for forming the magnetic layer, the non-magneticlayer or the back coating layer can generally include at least akneading step, a dispersing step, and a mixing step provided before andafter these steps, in a case where necessary. Each step may be dividedinto two or more stages. Various components used in the preparation ofeach layer forming composition may be added at the beginning or duringany step. In addition, each component may be separately added in two ormore steps. For example, a binding agent may be separately added in akneading step, a dispersing step, and a mixing step for adjustingviscosity after the dispersion. In the manufacturing step of themagnetic tape, a well-known manufacturing technology of the related artcan be used as a part of step. In the kneading step, an open kneader, acontinuous kneader, a pressure kneader, or a kneader having a strongkneading force such as an extruder can be used. The details of thekneading step are disclosed in JP1989-106338A (JP-H01-106338A) andJP1989-79274A (JP-H01-79274A). As a disperser, various well-knowndispersers using a shear force such as a beads mill, a ball mill, a sandmill, or a homogenizer can be used. In the dispersion, the dispersionbeads can be preferably used. As dispersion beads, ceramic beads orglass beads are used and zirconia beads are preferable. A combination oftwo or more kinds of beads may be used. A bead diameter (particlediameter) and a bead filling percentage of the dispersion beads are notparticularly limited and may be set according to powder which is adispersion target. Each layer forming composition may be filtered by awell-known method before performing the coating step. The filtering canbe performed by using a filter, for example. As the filter used in thefiltering, a filter having a hole diameter of 0.01 to 3 μm (for example,filter made of glass fiber or filter made of polypropylene) can be used,for example.

Coating Step

The magnetic layer can be formed by directly applying the magnetic layerforming composition onto the surface of the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. The back coating layer can be formed by applying the back coatinglayer forming composition onto the surface of the non-magnetic supportopposite to the surface provided with the non-magnetic layer and/or themagnetic layer (or non-magnetic layer and/or the magnetic layer is to beprovided). For details of the coating for forming each layer, adescription disclosed in a paragraph 0066 of JP2010-231843A can bereferred to.

Other Steps

For various other steps for manufacturing the magnetic tape, awell-known technology can be applied. For details of the various steps,descriptions disclosed in paragraphs 0067 to 0070 of JP2010-231843A canbe referred to, for example. For example, the coating layer of themagnetic layer forming composition can be subjected to an alignmentprocess in an alignment zone, while the coating layer is wet. For thealignment process, various well-known technologies disclosed in aparagraph 0052 of JP2010-24113A can be applied. For example, ahomeotropic alignment process can be performed by a well-known methodsuch as a method using a different polar facing magnet. In the alignmentzone, a drying speed of the coating layer can be controlled by atemperature and an air flow of the dry air and/or a transporting rate inthe alignment zone. In addition, the coating layer may be preliminarilydried before transporting to the alignment zone. As an example, themagnetic field strength in a homeotropic alignment process can be 0.1 to1.5 T.

Regarding the magnetic tape, a long magnetic tape raw material can beobtained through various steps. The obtained magnetic tape raw materialis cut (slit) by a well-known cutter to have a width of a magnetic tapeto be wound around the magnetic tape cartridge. The width is determinedaccording to the standard and is, for example, ½ inches. ½ inches=12.65mm. Generally, in the magnetic tape obtained by slitting, a servopattern can be formed. The formation of the servo pattern will bedescribed later in detail.

Heat Treatment

In the one embodiment, the magnetic tape can be a magnetic tapemanufactured through the following heat treatment. In anotherembodiment, the magnetic tape can be manufactured without the followingheat treatment. The performing of the following heat treatment cancontribute to the increase of the value of the medium life. This ismainly because it is considered that the following heat treatmentcontributes to suppression of the deformation of the magnetic tapemainly occurring due to the stress received during the storage in themagnetic tape cartridge.

As the heat treatment, the magnetic tape slit and cut to have a widthdetermined according to the standard described above can be wound arounda core member and can be subjected to the heat treatment in the woundstate.

In the one embodiment, the heat treatment is performed in a state wherethe magnetic tape is wound around the core member for heat treatment(hereinafter, referred to as a “winding core for heat treatment”), themagnetic tape after the heat treatment is wound around a cartridge reelof the magnetic tape cartridge, and a magnetic tape cartridge in whichthe magnetic tape is wound around the cartridge reel can bemanufactured.

The winding core for heat treatment can be formed of metal, a resin, orpaper. The material of the winding core for heat treatment is preferablya material having high stiffness, from a viewpoint of preventing theoccurrence of a winding defect such as spoking or the like. From thisviewpoint, the winding core for heat treatment is preferably formed ofmetal or a resin. In addition, as an indicator for stiffness, a bendingelastic modulus of the material for the winding core for heat treatmentis preferably equal to or greater than 0.2 GPa and more preferably equalto or greater than 0.3 GPa. Meanwhile, since the material having highstiffness is normally expensive, the use of the winding core for heattreatment of the material having stiffness exceeding the stiffnesscapable of preventing the occurrence of the winding defect causes thecost increase. By considering the viewpoint described above, the bendingelastic modulus of the material for the winding core for heat treatmentis preferably equal to or smaller than 250 GPa. In addition, the windingcore for heat treatment can be a solid or hollow core member. In a caseof a hollow shape, a wall thickness is preferably equal to or greaterthan 2 mm, from a viewpoint of maintaining the stiffness. In addition,the winding core for heat treatment may include or may not include aflange.

The magnetic tape having a length equal to or greater than a length tobe finally accommodated in the magnetic tape cartridge (hereinafter,referred to as a “final product length”) is prepared as the magnetictape wound around the winding core for heat treatment, and it ispreferable to perform the heat treatment by placing the magnetic tape inthe heat treatment environment, in a state where the magnetic tape iswound around the winding core for heat treatment. The magnetic tapelength wound around the winding core for heat treatment is equal to orgreater than the final product length, and is preferably the “finalproduct length+α”, from a viewpoint of ease of winding around thewinding core for heat treatment. This α is preferably equal to orgreater than 5 m, from a viewpoint of ease of the winding. The tensionin a case of winding around the winding core for heat treatment ispreferably equal to or greater than 0.10 N. In addition, from aviewpoint of preventing the occurrence of excessive deformation duringthe manufacturing, the tension in a case of winding around the windingcore for heat treatment is preferably equal to or smaller than 1.50 Nand more preferably equal to or smaller than 1.00 N. An outer diameterof the winding core for heat treatment is preferably equal to or greaterthan 20 mm and more preferably equal to or greater than 40 mm, fromviewpoints of ease of the winding and preventing coiling (curl inlongitudinal direction). The outer diameter of the winding core for heattreatment is preferably equal to or smaller than 100 mm and morepreferably equal to or smaller than 90 mm. A width of the winding corefor heat treatment may be equal to or greater than the width of themagnetic tape wound around this winding core. In addition, after theheat treatment, in a case of detaching the magnetic tape from thewinding core for heat treatment, it is preferable that the magnetic tapeand the winding core for heat treatment are sufficiently cooled andmagnetic tape is detached from the winding core for heat treatment, inorder to prevent the occurrence of the tape deformation which is notintended during the detaching operation. It is preferable the detachedmagnetic tape is wound around another winding core temporarily (referredto as a “winding core for temporary winding”), and the magnetic tape iswound around a cartridge reel (generally, an outer diameter isapproximately 40 to 50 mm) of the magnetic tape cartridge from thewinding core for temporary winding. Accordingly, a relationship betweenthe inside and the outside with respect to the winding core for heattreatment of the magnetic tape in a case of the heat treatment can bemaintained and the magnetic tape can be wound around the cartridge reelof the magnetic tape cartridge. Regarding the details of the windingcore for temporary winding and the tension in a case of winding themagnetic tape around the winding core, the description described aboveregarding the winding core for heat treatment can be referred to. In anembodiment in which the heat treatment is subjected to the magnetic tapehaving a length of the “final product length+α”, the lengthcorresponding to “+α” may be cut in any stage. For example, in oneembodiment, the magnetic tape having the final product length may bewound around the reel of the magnetic tape cartridge from the windingcore for temporary winding and the remaining length corresponding the“+α” may be cut. From a viewpoint of decreasing the amount of theportion to be cut out and removed, the α is preferably equal to orsmaller than 20 m.

The specific embodiment of the heat treatment performed in a state ofbeing wound around the core member as described above is describedbelow.

An atmosphere temperature for performing the heat treatment(hereinafter, referred to as a “heat treatment temperature”) ispreferably equal to or higher than 40° C. and more preferably equal toor higher than 50° C. On the other hand, from a viewpoint of preventingthe excessive deformation, the heat treatment temperature is preferablyequal to or lower than 75° C., more preferably equal to or lower than70° C., and even more preferably equal to or lower than 65° C.

A weight absolute humidity of the atmosphere for performing the heattreatment is preferably equal to or greater than 0.1 g/kg Dry air andmore preferably equal to or greater than 1 g/kg Dry air. The atmospherein which the weight absolute humidity is in the range described above ispreferable, because it can be prepared without using a special devicefor decreasing moisture. On the other hand, the weight absolute humidityis preferably equal to or smaller than 70 g/kg Dry air and morepreferably equal to or smaller than 66 g/kg Dry air, from a viewpoint ofpreventing a deterioration in workability by dew condensation. The heattreatment time is preferably equal to or longer than 0.3 hours and morepreferably equal to or longer than 0.5 hours. In addition, the heattreatment time is preferably equal to or shorter than 48 hours, from aviewpoint of production efficiency.

Formation of Servo Pattern

The magnetic tape has a plurality of servo bands in the magnetic layer.The servo band is configured of servo patterns continuous in thelongitudinal direction of the magnetic tape. The servo pattern canenable tracking control of the magnetic head, control of the runningspeed of the magnetic tape, and the like in the magnetic recording andreproducing device. The “formation of the servo pattern” can be“recording of a servo signal”. For example, the dimension information ofthe magnetic tape in the width direction during the running can beobtained using a servo signal, and the dimension of the magnetic tape inthe width direction can be controlled by adjusting and changing thetension applied in the longitudinal direction of the magnetic tapeaccording to the obtained dimension information.

The formation of the servo pattern will be described below.

The servo pattern is generally formed along a longitudinal direction ofthe magnetic tape. As a system of control using a servo signal (servocontrol), timing-based servo (TBS), amplitude servo, or frequency servois used.

As shown in European Computer Manufacturers Association (ECMA)-319 (June2001), a timing-based servo system is used in a magnetic tape based on alinear-tape-open (LTO) standard (generally referred to as an “LTOtape”). In this timing-based servo system, the servo pattern isconfigured by continuously disposing a plurality of pairs of magneticstripes (also referred to as “servo stripes”) not parallel to each otherin a longitudinal direction of the magnetic tape. The servo system is asystem of performing head tracking using a servo signal. In theinvention and the specification, the “timing-based servo pattern” refersto a servo pattern that enables head tracking in a servo system of atiming-based servo system. As described above, a reason for that theservo pattern is configured with one pair of magnetic stripes notparallel to each other is because a servo signal reading element passingon the servo pattern recognizes a passage position thereof.Specifically, one pair of the magnetic stripes are formed so that aspacing thereof is continuously changed along the width direction of themagnetic tape, and a relative position of the servo pattern and theservo signal reading element can be recognized, by the reading of thespacing thereof by the servo signal reading element. The information ofthis relative position can realize the tracking of a data track.Accordingly, a plurality of servo tracks are generally set on the servopattern along the width direction of the magnetic tape.

The servo band is configured of servo patterns continuous in thelongitudinal direction of the magnetic tape. The magnetic tape has aplurality of servo hands in the magnetic layer. For example, the numberthereof is 5 in the LTO tape. A region interposed between two adjacentservo bands is a data band. The data band is configured of a pluralityof data tracks and each data track corresponds to each servo track.

In one embodiment, as shown in JP2004-318983A, information showing thenumber of servo bands (also referred to as “servo band identification(ID)” or “Unique Data Band Identification Method (UDIM) information”) isembedded in each servo band. This servo band ID is recorded by shiftinga specific servo stripe among the plurality of pairs of servo stripes inthe servo band so that the position thereof is relatively displaced inthe longitudinal direction of the magnetic tape. Specifically, theposition of the shifted specific servo stripe among the plurality ofpairs of servo stripes is changed for each servo band. Accordingly, therecorded servo band ID becomes unique for each servo band, andtherefore, the servo band can be uniquely specified by only reading oneservo band by the servo signal reading element.

In a method of uniquely specifying the servo band, a staggered method asshown in ECMA-319 (June 2001) is used. In this staggered method, aplurality of the groups of one pair of magnetic stripes (servo stripe)not parallel to each other which are continuously disposed in thelongitudinal direction of the magnetic tape is recorded so as to beshifted in the longitudinal direction of the magnetic tape for eachservo band. A combination of this shifted servo band between theadjacent servo bands is set to be unique in the entire magnetic tape,and accordingly, the servo band can also be uniquely specified byreading of the servo pattern by two servo signal reading elements.

In addition, as shown in ECMA-319 (June 2001), information showing theposition in the longitudinal direction of the magnetic tape (alsoreferred to as “Longitudinal Position (LPOS) information”) is normallyembedded in each servo band. This LPOS information is recorded so thatthe position of one pair of servo stripes is shifted in the longitudinaldirection of the magnetic tape, in the same manner as the UDIMinformation. However, unlike the UDIM information, the same signal isrecorded on each servo band in this LPOS information.

Other information different from the UDIM information and the LPOSinformation can be embedded in the servo band. In this case, theembedded information may be different for each servo band as the UDIMinformation, or may be common in all of the servo bands, as the LPOSinformation.

In addition, as a method of embedding the information in the servo band,a method other than the method described above can be used. For example,a predetermined code may be recorded by thinning out a predeterminedpair among the group of pairs of the servo stripes.

A servo pattern forming head is also referred to as a servo write head.The servo write head generally includes pairs of gaps corresponding tothe pairs of magnetic stripes by the number of servo bands. In general,a core and a coil are respectively connected to each of the pairs ofgaps, and a magnetic field generated in the core can generate leakagemagnetic field in the pairs of gaps, by supplying a current pulse to thecoil. In a case of forming the servo pattern, by inputting a currentpulse while causing the magnetic tape to run on the servo write head,the magnetic pattern corresponding to the pair of gaps is transferred tothe magnetic tape, and the servo pattern can be formed. A width of eachgap can be suitably set in accordance with a density of the servopattern to be formed. The width of each gap can be set as, for example,equal to or smaller than 1 μm, 1 to 10 μm, or equal to or greater than10 μm.

Before forming the servo pattern on the magnetic tape, a demagnetization(erasing) process is generally performed on the magnetic tape. Thiserasing process can be performed by applying a uniform magnetic field tothe magnetic tape by using a DC magnet and an AC magnet. The erasingprocess includes direct current (DC) erasing and alternating current(AC) erasing. The AC erasing is performed by slowing decreasing anintensity of the magnetic field, while reversing a direction of themagnetic field applied to the magnetic tape. Meanwhile, the DC erasingis performed by applying the magnetic field in one direction to themagnetic tape. The DC erasing further includes two methods. A firstmethod is horizontal DC erasing of applying the magnetic field in onedirection along a longitudinal direction of the magnetic tape. A secondmethod is vertical DC erasing of applying the magnetic field in onedirection along a thickness direction of the magnetic tape. The erasingprocess may be performed with respect to all of the magnetic tape or maybe performed for each servo band of the magnetic tape.

A direction of the magnetic field to the servo pattern to be formed isdetermined in accordance with the direction of erasing. For example, ina case where the horizontal DC erasing is performed to the magnetictape, the formation of the servo pattern is performed so that thedirection of the magnetic field and the direction of erasing is oppositeto each other. Accordingly, the output of the servo signal obtained bythe reading of the servo pattern can be increased. As disclosed inJP2012-53940A, in a case where the magnetic pattern is transferred tothe magnetic tape subjected to the vertical DC erasing by using the gap,the servo signal obtained by the reading of the formed servo pattern hasa unipolar pulse shape. Meanwhile, in a case where the magnetic patternis transferred to the magnetic tape subjected to the horizontal DCerasing by using the gap, the servo signal obtained by the reading ofthe formed servo pattern has a bipolar pulse shape.

Generally, after forming the servo pattern, the magnetic tape is woundaround the reel hub of the cartridge reel and accommodated in themagnetic tape cartridge.

Vertical Squareness Ratio

In the one embodiment, the vertical squareness ratio of the magnetictape can be, for example, 0.55 or more, and is preferably 0.60 or more.It is preferable that the vertical squareness ratio of the magnetic tapeis 0.60 or more, from a viewpoint of improving the electromagneticconversion characteristics. In principle, an upper limit of thesquareness ratio is 1.00 or less. The vertical squareness ratio of themagnetic tape can be 1.00 or less, 0.95 or less, 0.90 or less, 0.85 orless, or 0.80 or less. It is preferable that the value of the verticalsquareness ratio of the magnetic tape is large from a viewpoint ofimproving the electromagnetic conversion characteristics. The verticalsquareness ratio of the magnetic tape can be controlled by a well-knownmethod such as performing a homeotropic alignment process.

In the invention and the specification, the “vertical squareness ratio”is squareness ratio measured in the vertical direction of the magnetictape. The “vertical direction” described with respect to the squarenessratio is a direction orthogonal to the surface of the magnetic layer,and can also be referred to as a thickness direction. In the inventionand the specification, the vertical squareness ratio is obtained by thefollowing method.

A sample piece having a size that can be introduced into an oscillationsample type magnetic-flux meter is cut out from the magnetic tape to bemeasured. Regarding the sample piece, using the oscillation sample typemagnetic-flux meter, a magnetic field is applied to a vertical directionof a sample piece (direction orthogonal to the surface of the magneticlayer) with a maximum applied magnetic field of 3979 kA/m, a measurementtemperature of 296 K, and a magnetic field sweep speed of 8.3 kA/m/sec,and a magnetization strength of the sample piece with respect to theapplied magnetic field is measured. The measured value of themagnetization strength is obtained as a value after diamagnetic fieldcorrection and a value obtained by subtracting magnetization of a sampleprobe of the oscillation sample type magnetic-flux meter as backgroundnoise. In a case where the magnetization strength at the maximum appliedmagnetic field is Ms and the magnetization strength at zero appliedmagnetic field is Mr, the squareness ratio SQ is a value calculated asSQ=Mr/Ms. The measurement temperature is referred to as a temperature ofthe sample piece, and by setting the ambient temperature around thesample piece to a measurement temperature, the temperature of the samplepiece can be set to the measurement temperature by realizing temperatureequilibrium.

Magnetic Head

According to another aspect of the invention, there is provided amagnetic recording and reproducing device comprising the magnetic tapecartridge. In the invention and the specification, the “magneticrecording and reproducing device” means a device capable of performingat least one of the recording of data on the magnetic tape or thereproducing of data recorded on the magnetic tape. The device iscommonly referred to as a drive and typically includes a magnetic head.The magnetic tape cartridge can be inserted into the magnetic recordingand reproducing device, and the magnetic tape can be run in the magneticrecording and reproducing device to record data on the magnetic tapeand/or reproduce the recorded data by the magnetic head. The magnetichead included in the magnetic recording and reproducing device can be arecording head capable of performing the recording of data on themagnetic tape, and can also be a reproducing head capable of performingthe reproducing of data recorded on the magnetic tape. In addition, inthe embodiment, the magnetic recording and reproducing device caninclude both of a recording head and a reproducing head as separatemagnetic heads. In another embodiment, the magnetic head included in themagnetic recording and reproducing device may have a configuration inwhich both the recording element and the reproducing element arecomprised in one magnetic head. As the reproducing head, a magnetic head(MR head) including a magnetoresistive (MR) element capable of readinginformation recorded on the magnetic tape with excellent sensitivity asthe reproducing element is preferable. As the MR head, variouswell-known MR heads (for example, a Giant Magnetoresistive (GMR) head,or a Tunnel Magnetoresistive (TMR) head) can be used. In addition, themagnetic head which performs the recording of data and/or thereproducing of data may include a servo pattern reading element.Alternatively, as a head other than the magnetic head which performs therecording of data and/or the reproducing of data, a magnetic head (servohead) including a servo pattern reading element may be included in themagnetic recording and reproducing device. For example, the magnetichead which performs the recording of data and/or reproducing of therecorded data (hereinafter, also referred to as a “recording andreproducing head”) can include two servo signal reading elements, andeach of the two servo signal reading elements can read two adjacentservo bands with the data band interposed therebetween at the same time.One or a plurality of elements for data can he disposed between the twoservo signal reading elements. The element for recording data (recordingelement) and the element for reproducing data (reproducing element) arecollectively referred to as “elements for data”.

By reproducing data using the reproducing element having a narrowreproducing element width as the reproducing element, the data recordedat high density can be reproduced with high sensitivity. From thisviewpoint, the reproducing element width of the reproducing element ispreferably 0.8 μm or less. The reproducing element width of thereproducing element can be, for example, 0.1 μm or more. However, it isalso preferable to fall below this value from the above viewpoint.

On the other hand, as the reproducing element width decreases, aphenomenon such as reproducing failure due to off-track is more likelyto occur. In order to suppress the occurrence of such a phenomenon, itis preferable to use a magnetic recording and reproducing device thatcontrols the dimension of the magnetic tape in the width direction byadjusting and changing the tension applied in the longitudinal directionof the magnetic tape during the running.

Here, the “reproducing element width” refers to a physical dimension ofthe reproducing element width. Such physical dimensions can be measuredwith an optical microscope, a scanning electron microscope, or the like.

In a case of recording data and/or reproducing recorded data, first,head tracking can be performed using a servo signal. That is, as theservo signal reading element follows a predetermined servo track, theelement for data can be controlled to pass on the target data track. Themovement of the data track is performed by changing the servo track tobe read by the servo signal reading element in the tape width direction.

In addition, the recording and reproducing head can perform therecording and/or reproducing with respect to other data bands. In thiscase, the servo signal reading element is moved to a predetermined servoband by using the UDIM information described above, and the trackingwith respect to the servo band may be started.

FIG. 5 shows an example of disposition of data bands and servo bands. InFIG. 5, a plurality of servo bands 1 are disposed to be interposedbetween guide bands 3 in a magnetic layer of a magnetic tape MT. Aplurality of regions 2 each of which is interposed between two servobands are data bands. The servo pattern is a magnetized region and isformed by magnetizing a specific region of the magnetic layer by a servowrite head. The region magnetized by the servo write head (positionwhere a servo pattern is formed) is determined by standards. Forexample, in an LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 6 are formed on a servo band, in a case ofmanufacturing a magnetic tape. Specifically, in FIG. 6, a servo frame SFon the servo band 1 is configured with a servo sub-frame 1 (SSF1) and aservo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with an Aburst (in FIG. 6, reference numeral A) and a B burst (in FIG. 6,reference numeral B). The A burst is configured with servo patterns A1to A5 and the B burst is configured with servo patterns B1 to B5.Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG.6, reference numeral C) and a D burst (in FIG. 6, reference numeral D).The C burst is configured with servo patterns C1 to C4 and the D burstis configured with servo patterns D1 to D4. Such 18 servo patterns aredisposed in the sub-frames in the arrangement of 5, 5, 4, 4, as the setsof 5 servo patterns and 4 servo patterns, and are used for identifyingthe servo frames. FIG. 6 shows one servo frame for explaining. However,in practice, in the magnetic layer of the magnetic tape in which thehead tracking in the timing-based servo system is performed, a pluralityof servo frames are disposed in each servo band in a running direction.In FIG. 6, an arrow shows the running direction. For example, an LTOUltrium format tape generally includes 5,000 or more servo frames per atape length of 1 m, in each servo band of the magnetic layer.

Examples

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to the embodiments shown in theexamples. “Parts” and “%” in the following description mean “parts bymass” and “% by mass”, unless otherwise noted. “eq” indicates equivalentand a unit not convertible into SI unit.

In addition, various steps and operations described below were performedin an environment of a temperature of 20° C. to 25° C. and a relativehumidity of 40% to 60%, unless otherwise noted.

Non-Magnetic Support

In Table 1, “PEN” indicates a polyethylene naphthalate support, “PET”indicates a polyethylene terephthalate support, and “PA” indicates anaromatic polyamide support. The moisture content and the Young's modulusin Table 1 is a value measured by the method described above.

Ferromagnetic Powder

In Table 1, “BaFe” in a column of the type of the ferromagnetic powderis a hexagonal barium ferrite powder having an average particle size(average plate diameter) of 21 nm.

In Table 1, “SrFe1” of the column of the type of ferromagnetic powderindicates a hexagonal strontium ferrite powder produced as follows.

1,707 g of SrCO₃, 687 g of H₃BO₃, 1,120 g of Fe₂O₃, 45 g of Al(OH)₃, 24g of BaCO₃, 13 g of CaCO₃, and 235 g of Nd₂O₃ were weighed and mixed ina mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,390° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the prepared amorphous body was put into an electronic furnace,heated to 635° C. (crystallization temperature) at a rate of temperaturerise of 3.5° C./min, and held at the same temperature for 5 hours, andhexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1,000 g of zirconia beads having a particle diameter of 1 mm,and 800 mL of an acetic acid aqueous solution having a concentration of1% were added to a glass bottle, and a dispersion process was performedin a paint shaker for 3 hours. After that, the obtained dispersionliquid and the beads were separated and put in a stainless still beaker.The dispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 18 nm, an activation volume was 902nm³, an anisotropy constant Ku was 2.2×10⁵ J/m³, and a massmagnetization σs was 49 A×m²/kg.

12 mg of a sample powder was collected from the hexagonal strontiumferrite powder obtained as described above, the element analysis of afiltrate obtained by the partial dissolving of this sample powder underthe dissolving conditions described above was performed by the ICPanalysis device, and a surface layer portion content of a neodymium atomwas obtained.

Separately, 12 mg of a sample powder was collected from the hexagonalstrontium ferrite powder obtained as described above, the elementanalysis of a filtrate obtained by the total dissolving of this samplepowder under the dissolving conditions described above was performed bythe ICP analysis device, and a bulk content of a neodymium atom wasobtained.

The content (bulk content) of the neodymium atom in the hexagonalstrontium ferrite powder obtained as described above with respect to 100atom % of iron atom was 2.9 atom %. In addition, the surface layerportion content of the neodymium atom was 8.0 atom %. A ratio of thesurface layer portion content and the bulk content, “surface layerportion content/bulk content” was 2.8 and it was confirmed that theneodymium atom is unevenly distributed on the surface layer of theparticles.

A crystal structure of the hexagonal ferrite shown by the powderobtained as described above was confirmed by scanning CuKa ray under theconditions of a voltage of 45 kV and intensity of 40 mA and measuring anX-ray diffraction pattern under the following conditions (X-raydiffraction analysis). The powder obtained as described above showed acrystal structure of magnetoplumbite type (M type) hexagonal ferrite. Inaddition, a crystal phase detected by the X-ray diffraction analysis wasa magnetoplumbite type single phase.

PANalytical X'Pert Pro diffractometer, PIXcel detector

Soller slit of incident beam and diffraction beam: 0.017 radians

Fixed angle of dispersion slit: ¼ degrees

Mask: 10 mm

Scattering prevention slit: ¼ degrees

Measurement mode: continuous

Measurement time per 1 stage: 3 seconds

Measurement speed: 0.017 degrees per second

Measurement step: 0.05 degree

In Table 1, “SrFe2” of the column of the type of ferromagnetic powderindicates a hexagonal strontium ferrite powder produced as follows.

1,725 g of SrCO₃, 666 g of H₃BO₃, 1,332 g of Fe₂O₃, 52 g of Al(OH)₃, 34g of CaCO₃, and 141 g of BaCO₃ were weighed and mixed in a mixer toobtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,380° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the obtained amorphous body was put into an electronic furnace,heated to 645° C. (crystallization temperature), and held at the sametemperature for 5 hours, and hexagonal strontium ferrite particles wereprecipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1,000 g of zirconia beads having a particle diameter of 1 mm,and 800 mL of an acetic acid aqueous solution having a concentration of1% were added to a glass bottle, and a dispersion process was performedin a paint shaker for 3 hours. After that, the obtained dispersionliquid and the beads were separated and put in a stainless still beaker.The dispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 19 nm, an activation volume was1,102 nm³, an anisotropy constant Ku was 2.0×10⁵ J/m³, and a massmagnetization σs was 50 A×m²/kg.

In Table 1, “ε-iron oxide” of the column of the type of ferromagneticpowder indicates an ε-iron oxide powder produced as follows.

4.0 g of ammonia aqueous solution having a concentration of 25% wasadded to a material obtained by dissolving 8.3 g of iron (III) nitratenonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg ofcobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and1.5 g of polyvinyl pyrrolidone (PVP) in 90 g of pure water, whilestirring by using a magnetic stirrer, in an atmosphere under theconditions of an atmosphere temperature of 25° C., and the mixture wasstirred for 2 hours still under the temperature condition of theatmosphere temperature of 25° C. An aqueous solution of citric acidobtained by dissolving 1 g of citric acid in 9 g of pure water was addedto the obtained solution and stirred for 1 hour. The powder precipitatedafter the stirring was collected by centrifugal separation, washed withpure water, and dried in a heating furnace at a furnace innertemperature of 80° C.

800 g of pure water was added to the dried powder and the powder wasdispersed in water again, to obtain a dispersion liquid. The obtaineddispersion liquid was heated to a liquid temperature of 50° C., and 40 gof ammonia aqueous solution having a concentration of 25% was addeddropwise while stirring. The stirring was performed for 1 hour whileholding the temperature of 50° C., and 14 mL of tetraethoxysilane (TEOS)was added dropwise and stirred for 24 hours. 50 g of ammonium sulfatewas added to the obtained reaction solution, the precipitated powder wascollected by centrifugal separation, washed with pure water, and driedin a heating furnace at a furnace inner temperature of 80° C. for 24hours, and a precursor of ferromagnetic powder was obtained.

The heating furnace at a furnace inner temperature of 1,000° C. wasfilled with the obtained precursor of ferromagnetic powder in theatmosphere and subjected to heat treatment for 4 hours.

The heat-treated precursor of ferromagnetic powder was put into sodiumhydroxide (NaOH) aqueous solution having a concentration of 4 mol/L, theliquid temperature was held at 70° C., stirring was performed for 24hours, and accordingly, a silicon acid compound which was an impuritywas removed from the heat-treated precursor of ferromagnetic powder.

After that, by the centrifugal separation process, ferromagnetic powderobtained by removing the silicon acid compound was collected and washedwith pure water, and ferromagnetic powder was obtained.

The composition of the obtained ferromagnetic powder was confirmed byInductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), andGa, Co, and Ti substitution type ε-iron oxide(ε-Ga_(0.28)Co_(0.05)Ti_(0.05)Fe_(1.62)O₃) was obtained. In addition,the X-ray diffraction analysis was performed under the same conditionsas the conditions described regarding the hexagonal strontium ferritepowder SrFe1 in advance, and it was confirmed that the obtainedferromagnetic powder has a crystal structure of a single phase which isan ε phase not including a crystal structure of an α phase and a γ phase(ε-iron oxide type crystal structure) from the peak of the X-raydiffraction pattern.

Regarding the obtained ε-iron oxide powder, an average particle size was12 nm, an activation volume was 746 nm³, an anisotropy constant Ku was1.2×10⁵ J/m³, and a mass magnetization σs was 16 A×m²/kg.

The activation volume and the anisotropy constant Ku of the hexagonalstrontium ferrite powder and the ε-iron oxide powder are values obtainedby the method described above regarding each ferromagnetic powder byusing an oscillation sample type magnetic-flux meter (manufactured byToei Industry Co., Ltd.).

In addition, the mass magnetization σs is a value measured at themagnetic field strength of 1,194 kA/m (15 kOe) by using an oscillationsample type magnetic-flux meter (manufactured by Toei Industry Co.,Ltd.).

Example 1 (1) Preparation of Alumina Dispersion

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixedsolvent of methyl ethyl ketone and toluene) of a polyester polyurethaneresin including a SO₃Na group as a polar group (UR-4800 manufactured byToyobo Co., Ltd. (polar group amount: 80 meq/kg)), and 570.0 parts of amixed solvent solution of methyl ethyl ketone and cyclohexanone (massratio of 1:1) as a solvent were mixed with 100.0 parts of alumina powder(HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) having agelatinization ratio of approximately 65% and a Brunauer-Emmett-Teller(BET) specific surface area of 20 m²/g, and dispersed in the presence ofzirconia beads by a paint shaker for 5 hours. After the dispersion, thedispersion liquid and the beads were separated by a mesh and an aluminadispersion was obtained.

(2) Magnetic Layer Forming Composition List

Magnetic Liquid

Ferromagnetic powder (see Table 1): 100.0 parts

SO₃Na group-containing polyurethane resin: 14.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Cyclohexanone: 150.0 parts

Methyl ethyl ketone: 150.0 parts

Abrasive Solution

Alumina dispersion prepared in the section (1): 6.0 parts

Silica sol (projection formation agent liquid)

Colloidal silica (Average particle size: 120 nm): 2.0 parts

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Stearic acid amide: 0.2 parts

Butyl stearate: 2.0 parts

Polyisocyanate (CORONATE (registered product) L manufactured by TosohCorporation): 2.5 parts

Finishing Additive Solvent

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

(3) Non-Magnetic Layer Forming Composition List

Non-magnetic inorganic powder: α-iron oxide: 100.0 parts

Average particle size (average major axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

Carbon black: 20.0 parts

Average particle size: 20 nm

SO₃Na group-containing polyurethane resin: 18.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Stearic acid: 2.0 parts

Stearic acid amide: 0.2 parts

Butyl stearate: 2.0 parts

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

(4) Back Coating Layer Forming Composition List

Carbon black: 100.0 parts

DBP (Dibutyl phthalate) oil absorption: 74 cm³/100 g

Nitrocellulose: 27.0 parts

Polyester polyurethane resin including sulfonic acid group and/or saltthereof: 62.0 parts

Polyester resin: 4.0 parts

Alumina powder (BET specific surface area: 17 m²/g): 0.6 parts

Methyl ethyl ketone: 600.0 parts

Toluene: 600.0 parts

Polyisocyanate (CORONATE (registered product) L manufactured by TosohCorporation): 15.0 parts

(5) Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod. The magnetic liquid was prepared by dispersing(beads-dispersing) each component by using a batch type vertical sandmill for 24 hours. As dispersion beads, zirconia beads having a beaddiameter of 0.5 mm were used. The prepared magnetic liquid, the abrasivesolution, and other components (silica sol, other components, andfinishing additive solvent) were mixed with each other andbeads-dispersed for 5 minutes by using the sand mill, and the treatment(ultrasonic dispersion) was performed with a batch type ultrasonicdevice (20 kHz, 300 W) for 0.5 minutes. After that, the obtained mixedsolution was filtered by using a filter having a hole diameter of 0.5μm, and the magnetic layer forming composition was prepared.

The non-magnetic layer forming composition was prepared by the followingmethod. The components described above excluding the lubricant (stearicacid, stearic acid amide, and butyl stearate) were kneaded and dilutedby an open kneader, and subjected to a dispersion process with atransverse beads mill disperser. After that, the lubricant (stearicacid, stearic acid amide, and butyl stearate) was added, and stirred andmixed with a dissolver stirrer, and a non-magnetic layer formingcomposition was prepared.

The back coating layer forming composition was prepared by the followingmethod. The components excluding polyisocyanate were introduced in adissolver stirrer and stirred at a circumferential speed of 10 m/sec for30 minutes, and the dispersion process was performed with a transversebeads mill disperser. After that, polyisocyanate was added, and stirredand mixed with a dissolver stirrer, and a back coating layer formingcomposition was prepared.

(6) Manufacturing Method of Magnetic Tape and Magnetic Tape Cartridge

The non-magnetic layer forming composition prepared in the section (5)was applied to a surface of a biaxial stretched support having athickness of 4.0 μm described in Table 1 so that the thickness after thedrying becomes 1.0 μm and was dried to form a non-magnetic layer. Then,the magnetic layer forming composition prepared in the section (5)described above was applied onto the non-magnetic layer so that thethickness after the drying is 0.1 μm, and a coating layer was formed.After that, a homeotropic alignment process was performed by applying amagnetic field having a magnetic field strength of 0.3 T in a verticaldirection with respect to a surface of a coating layer, while thecoating layer of the magnetic layer forming composition is not dried.Then, the drying was performed to form the magnetic layer. After that,the back coating layer forming composition prepared in the section (5)described above was applied to the surface of the support on a sideopposite to the surface where the non-magnetic layer and the magneticlayer were formed, so that the thickness after the drying becomes 0.5μm, and was dried to form a back coating layer.

After that, a surface smoothing treatment (calender process) wasperformed by using a calender roll configured of only a metal roll, at aspeed of 100 m/min, linear pressure of 300 kg/cm), and a calendertemperature (surface temperature of a calender roll) of 90° C.

Then, the heat treatment was performed by storing the long magnetic taperaw material in a heat treatment furnace at the atmosphere temperatureof 70° C. (heat treatment time: 36 hours). After the heat treatment, themagnetic tape was obtained by slitting to have a width of ½ inches. Byrecording a servo signal on a magnetic layer of the obtained magnetictape with a commercially available servo writer, the magnetic tapeincluding a data band, a servo band, and a guide band in the dispositionaccording to a linear-tape-open (LTO) Ultrium format, and including aservo pattern (timing-based servo pattern) having the disposition andshape according to the LTO Ultrium format on the servo band wasobtained.

The servo pattern formed by doing so is a servo pattern disclosed inJapanese Industrial Standards (JIS) X6175:2006 and Standard ECMA-319(June 2001).

The total number of servo bands is five, and the total number of databands is four.

The magnetic tape (length of 970 m) after the servo pattern formationwas wound around the winding core for heat treatment, and the heattreatment was performed in a state of being wound around this windingcore. As the winding core for heat treatment, a solid core member (outerdiameter: 50 mm) formed of a resin and having 0.8 GPa of a bendingelastic modulus was used, and the tension in a case of the winding wasset as 0.60 N. The heat treatment was performed at the heat treatmenttemperature shown in Table 1 for 5 hours. The weight absolute humidityin the atmosphere in which the heat treatment was performed was 10 g/kgDry air.

After the heat treatment, the magnetic tape and the winding core forheat treatment were sufficiently cooled, the magnetic tape was detachedfrom the winding core for heat treatment and wound around the windingcore for temporary winding, and then, the magnetic tape having the finalproduct length (960 m) was wound around the reel hub of the reel of themagnetic tape cartridge from the winding core for temporary winding byapplying the tension having a value described in the section of “windingtension during manufacture” of Table 1 in the longitudinal direction ofthe magnetic tape, and the remaining length of 10 m was cut out and theleader tape based on section 9 of Standard European ComputerManufacturers Association (ECMA)-319 (June 2001) Section 3 was bonded tothe terminal of the cut side by using a commercially available splicingtape.

As the winding core for temporary winding, a solid core member havingthe same outer diameter and formed of the same material as the windingcore for heat treatment was used.

As the magnetic tape cartridge accommodating the magnetic tape describedabove, a single reel type magnetic tape cartridge having theconfiguration shown in FIG. 2 was used. The reel hub of this magnetictape cartridge is a single-layer structure reel hub (thickness: 2.5 mm,outer diameter: 44 mm) obtained by injection molding glass fiberreinforced polycarbonate. The glass fiber content of this glass fiberreinforced polycarbonate is the value (unit: % by mass) shown inTable 1. A part of the glass fiber reinforced polycarbonate forinjection molding was collected, and according to JIS K 7171: 2016section 6.3.1 (preparation from molding material), it is described inthe same JIS section 6.1.2. The recommended test pieces were prepared,and the bending elastic modulus (arithmetic mean of 5 test pieces) wascalculated according to the same JIS, and a value shown in Table 1 wasobtained. In the examples and comparative examples described below, thebending elastic modulus of the reel hub material was determined by theabove method. The bending elastic modulus of the winding core for heattreatment is also a value obtained in the same manner.

As described above, a single reel type magnetic tape cartridge ofExample 1 in which a magnetic tape having a length of 960 m was woundaround a reel was manufactured.

Examples 2 to 24 and Comparative Examples 1 to 9

A magnetic tape cartridge was produced by the method as in Example 1,except that various conditions shown in Table 1 were changed as shown insections of Table 1.

In the comparative examples in which “none” is described in the columnof “heat treatment temperature” in Table 1, the magnetic tape having afinal product length of 960 m was accommodated in the magnetic tapecartridge, without performing the heat treatment in a state of beingwound around the winding core for heat treatment.

For each of the above examples and comparative examples, two magnetictape cartridges were produced, one was used for the evaluation of thefollowing medium life and tape thickness, and the other one was used forthe evaluation of the recording and reproducing performance which willbe described later.

Evaluation Method Medium Life Measurement of Servo Band Spacing

The magnetic tape cartridge to be measured was placed in a measurementenvironment of an atmosphere temperature of 23° C. and a relativehumidity of 50% for 5 days in order to make it familiar with themeasurement environment.

After that, in the measurement environment, in the magnetic recordingand reproducing device shown in FIG. 1, the magnetic tape was allowed torun in a state where a tension of 0.70 N was applied in the longitudinaldirection of the magnetic tape. For such running, the spacing betweentwo servo bands adjacent to each other with a data band interposedtherebetween was measured at spacing of 1 m over the entire length ofthe magnetic tape. The measurement was made for all servo band spacings.The servo band spacing measured in this way was referred to as a “servoband spacing before storage” at each measurement position. The spacingbetween two servo bands adjacent to each other with the data bandinterposed therebetween was calculated as follows.

In order to obtain the spacing between two servo bands adjacent to eachother with the data band interposed therebetween, the dimensions of theservo pattern are required. The standard of the dimension of the servopattern varies depending on generation of LTO. Therefore, first, anaverage distance AC between the corresponding four stripes of the Aburst and the C burst and an azimuth angle α of the servo pattern aremeasured using a magnetic force microscope or the like.

Next, the servo pattern formed on the magnetic tape is read sequentiallyalong the tape longitudinal direction by using a reel tester and a servohead including two servo signal reading elements fixed in the spacing inthe direction orthogonal to the longitudinal direction of the magnetictape (hereinafter, one is referred to as an upper side and the other oneis referred to as a lower side). An average time between 5 stripescorresponding to the A burst and the B burst over the length of 1 LPOSword is defined as a. An average time between 4 stripes corresponding tothe A burst and the C burst over the length of 1 m is defined as b. Atthis time, the value defined by AC×(½−a/b)/(2×tan(α)) represents areading position PES in the width direction based on the servo signalobtained by the servo signal reading element. The reading of the servopattern is simultaneously performed by the two upper side and lower sideservo signal reading elements. The value of the PES obtained by theupper side servo signal reading element is set as PES1, and the value ofthe PES obtained by the lower side servo signal reading element is setas PES2. As “PES2−PES1”, the spacing between two servo bands adjacent toeach other with the data band interposed therebetween can be obtained.This is because the upper side and lower side servo pattern readingelements are fixed to the servo head and their spacings do not change.

After that, for the magnetic tape cartridge, “servo band spacing afterstorage for 24 hours” and “A after storage for 24 hours”, “servo bandspacing after storage for 48 hours” and “A after storage for 48 hours”,“servo band spacing after storage for 72 hours”, “A after storage for 72hours”, and “servo band spacing after storage for 96 hours” and “A afterstorage for 96 hours”, and “servo band spacing after storage for 120hours” and “A after storage for 120 hours” were obtained by the methoddescribed above.

Derivation of Linear Function

From the value of A and the value of the logarithm log_(e)T of thestorage time T obtained in the step described above, a linear functionof A and log_(e)T was derived by the least squares method. The linearfunction is represented by Y=cX+d, where A is Y and log_(e)T is X. c andd were coefficients determined by the least squares method,respectively, and usually both thereof were positive values.

Determination of B

In the five environments (temperature of 16° C. and relative humidity of20%, temperature of 16° C. and relative humidity of 80%, temperature of26° C. and relative humidity of 80%, temperature of 32° C. and relativehumidity of 20%, and temperature of 32° C. and relative humidity of55%), the measurement was performed by the following method.

For each measurement environment, the magnetic tape cartridge to bemeasured was placed in the measurement environment for 5 days in orderto make it familiar with the measurement environment.

After that, in the measurement environment, in the magnetic recordingand reproducing device shown in FIG. 1, the magnetic tape was allowed torun in a state where a tension of 0.70 N was applied in the longitudinaldirection of the magnetic tape. The servo band spacing was measured bythe method described above in the data band 0 (zero) for the running at1 m spacing in region having a reel outer periphery of 100 m. Asdescribed above, an arithmetic mean of the measured servo band spacingswas the servo band spacing in the measurement environment.

After obtaining the servo band spacing in each of the five environmentsas described above, a value calculated as “(maximum value−minimumvalue)×½” using the maximum value and the minimum value among theobtained values was defined as “B” of the magnetic tape cartridge to bemeasured.

Calculation of Medium Life

The T in a case where A satisfies “Equation 1: A=1.5−B” was calculatedby the linear function of the A and the logarithm log_(e) T of T derivedabove. Table 1 shows the value of the medium life obtained in each ofthe examples and comparative examples.

Tape Thickness

The magnetic tape cartridge after the evaluation was placed in anenvironment with a temperature of 20° C. to 25° C. and a relativehumidity of 40% to 60% for 5 days or longer to make it familiar with theenvironment. Then, subsequently, in the same environment, 10 tapesamples (length: 5 cm) were cut out from any part of the magnetic tapetaken out from the magnetic tape cartridge, and these tape samples werestacked to measure the thickness. The thickness was measured using adigital thickness gauge of a Millimar 1240 compact amplifiermanufactured by MARH and a Millimar 1301 induction probe. The value(thickness per tape sample) obtained by calculating 1/10 of the measuredthickness was defined as the tape thickness. For each magnetic tape, thetape thickness was 5.6 μm.

Evaluation of Recording and Reproducing Performance

(1) Recording of data and reproducing of recorded data on magnetic tapeafter storage The recording and reproducing before storage wereperformed using the magnetic recording and reproducing device having theconfiguration shown in FIG. 1. The recording and reproducing headmounted on the recording and reproducing head unit has 32 or morechannels of reproducing elements (reproducing element width: 0.8 μm) andrecording elements, and servo signal reading and reproducing elements onboth sides thereof.

For each magnetic tape cartridge, the environment for recording and thereproducing which will be described later was an environment in whichthe servo band spacing obtained in the measurement for obtaining B wasthe maximum value among the five environments.

The magnetic tape cartridge was placed in the environment for performingthe reproducing for 5 days to make it familiar with the environment forperforming the recording. Then, in the same environment, the recordingwas performed as follows.

The magnetic tape cartridge was set in the magnetic recording andreproducing device and the magnetic tape was loaded. Next, whileperforming servo tracking, the recording and reproducing head unitrecords pseudo random data having a specific data pattern on themagnetic tape. The tension applied in the tape longitudinal direction atthat time is a constant value of 0.50 N. At the same time with therecording of the data, the value of the servo band spacing of the entiretape length was measured every 1 m of the longitudinal position andrecorded in the cartridge memory.

Next, while performing servo tracking, the recording and reproducinghead unit reproduces the data recorded on the magnetic tape. At thattime, the value of the servo band spacing was measured at the same timeas the reproducing, and the tension applied in the tape longitudinaldirection was changed so that an absolute value of a difference from theservo band spacing during the recording at the same longitudinalposition approaches 0 based on the information recorded in the cartridgememory. During the reproducing, the measurement of the servo bandspacing and the tension control based on it are continuously performedin real time. In a case of such reproducing, the tension applied in thelongitudinal direction of the magnetic tape was changed in a range of0.50 N to 0.85 N by the control device of the magnetic recording andreproducing device. Therefore, the maximum value of the tension appliedin the longitudinal direction of the magnetic tape during thereproducing is 0.85 N.

At the end of the reproducing, the entire length of the magnetic tapewas wound around the cartridge reel of the magnetic tape cartridge.

(2) Winding (Rewinding) Around Cartridge Reel and Storage

Subsequently, in the same environment, the magnetic tape was allowed torun in the magnetic recording and reproducing device and the entirelength of the magnetic tape was wound around the winding reel of themagnetic recording and reproducing device. The tension applied in thelongitudinal direction of the magnetic tape during the winding was setto a constant value of 0.40 N.

Then, tension was applied in the longitudinal direction of the magnetictape at a constant value of 0.40 N, and the entire length of themagnetic tape was wound on the cartridge reel (also referred to as“rewinding”).

After the rewinding, the magnetic tape cartridge accommodating themagnetic tape was stored for 24 hours in an environment with anatmosphere temperature of 60° C. and a relative humidity of 20% in orderto bring it closer to the state after long-term storage for severalyears.

(3) Evaluation of Recording and Reproducing Performance After Storage

After the storage, in order to make it familiar with the environment forperforming the reproducing, the magnetic tape cartridge was placed inthe environment in which the servo band spacing obtained in themeasurement for obtaining B was the maximum value among the fiveenvironments for 5 days. Then, in the same environment, the reproducingwas performed in the same manner as the reproducing before storage inthe section (1). That is, the reproducing was performed by changing thetension applied in the longitudinal direction of the magnetic tape asdescribed above.

The number of channels in the reproducing described above was 32channels, and in the reproducing after the storage, in a case where thedata of all 32 channels was correctly read, the recording andreproducing performance was evaluated as “4”, in a case where the dataof 31 channels or 30 channels was correctly read, the recording andreproducing performance was evaluated as “3”, in a case where the dataof 29 channels or 28 channels was correctly read, the recording andreproducing performance was evaluated as “2”, and in other cases, therecording and reproducing performance was evaluated as “1”.

The result described above is shown in Table 1 (Tables 1-1 to 1-3).

TABLE 1-1 Example Example Example Example Example Example Example Unit 12 3 4 5 6 7 Kind of ferromagnetic powder BaFe BaFe BaFe BaFe BaFe BaFeBaFe Kind of support PET PET PET PET PET PET PET Moisture content ofsupport % 0.8 0.8 0.8 0.8 0.8 0.8 0.1 (a) Young's modulus in widthdirection MPa 6000 6000 6000 6000 6000 6000 6000 of support (b) Young'smodulus in longitudinal MPa 8000 8000 8000 8000 8000 8000 8000 directionof support (b) − (a) MPa 2000 2000 2000 2000 2000 2000 2000 B μm 0.4 0.40.4 0.4 0.4 0.4 0.2 Heat treatment temperature ° C. 60° C. 60° C. 60° C.70° C. 70° C. 70° C. 60° C. Bending elastic modulus of reel hub GPa 5 55 5 5 5 5 material Glass fiber content of reel hub % 15 15 15 15 15 1515 material Winding tension during manufacture 0.40N 0.20N 0.10N 0.40N0.20N 0.10N 0.40N Medium life 3 years 10 years 50 years 15 years 40years 75 years 30 years Recording and reproducing 3 3 3 3 3 3 3performance Example Example Example Example Example Unit 8 9 10 11 12Kind of ferromagnetic powder BaFe BaFe BaFe BaFe BaFe Kind of supportPET PET PET PEN PEN Moisture content of support % 0.1 0.1 0.1 1.0 1.0(a) Young's modulus in width direction MPa 6000 6000 6000 5000 5000 ofsupport (b) Young's modulus in longitudinal MPa 8000 8000 8000 6000 6000direction of support (b) − (a) MPa 2000 2000 2000 1000 1000 B μm 0.2 0.20.2 0.5 0.5 Heat treatment temperature ° C. 70° C. 60° C. 70° C. 60° C.60° C. Bending elastic modulus of reel hub GPa 5 8 8 5 5 material Glassfiber content of reel hub % 15 30 30 15 15 material Winding tensionduring manufacture 0.10N 0.40N 0.10N 0.40N 0.20N Medium life 100 years40 years 120 years 10 years 30 years Recording and reproducing 4 3 4 3 3performance

TABLE 1-2 Example Example Example Example Example Example Example Unit13 14 15 16 17 18 19 Kind of ferromagnetic powder BaFe BaFe BaFe BaFeBaFe BaFe BaFe Kind of support PEN PEN PEN PEN PEN PEN PEN Moisturecontent of support % 1.0 1.0 1.0 1.0 0.1 0.1 0.1 (a) Young's modulus inwidth direction MPa 5000 5000 5000 5000 5000 5000 5000 of support (b)Young's modulus in longitudinal MPa 6000 6000 6000 6000 6000 6000 6000direction of support (b) − (a) MPa 1000 1000 1000 1000 1000 1000 1000 Bμm 0.5 0.5 0.5 0.5 0.3 0.3 0.3 Heat treatment temperature ° C. 60° C.70° C. 70° C. 70° C. 60° C. 70° C. 60° C. Bending elastic modulus ofreel hub GPa 5 5 5 5 5 5 8 material Glass fiber content of reel hub % 1515 15 15 15 15 30 material Winding tension during manufacture 0.10N0.40N 0.20N 0.10N 0.40N 0.10N 0.40N Medium life 50 years 15 years 40years 75 years 30 years 100 years 40 years Recording and reproducing 3 33 3 3 4 3 performance Example Example Example Example Example Unit 20 2122 23 24 Kind of ferromagnetic powder BaFe BaFe SrFe1 SrFe2 ε-Iron oxideKind of support PEN PA PET PET PET Moisture content of support % 0.1 2.00.8 0.8 0.8 (a) Young's modulus in width direction MPa 5000 10000 60006000 6000 of support (b) Young's modulus in longitudinal MPa 6000 120008000 8000 8000 direction of support (b) − (a) MPa 1000 2000 2000 20002000 B μm 0.3 0.1 0.4 0.4 0.4 Heat treatment temperature ° C. 70° C. 70°C. 60° C. 60° C. 60° C. Bending elastic modulus of reel hub GPa 8 8 5 55 material Glass fiber content of reel hub % 30 30 15 15 15 materialWinding tension during manufacture 0.10N 0.10N 0.40N 0.40N 0.40N Mediumlife 120 years 150 years 3 years 3 years 3 years Recording andreproducing 4 4 3 3 3 performance

TABLE 1-3 Comparative Comparative Comparative Comparative ComparativeUnit Example 1 Example 2 Example 3 Example 4 Example 5 Kind offerromagnetic powder BaFe BaFe BaFe BaFe BaFe Kind of support PET PETPET PEN PEN Moisture content of support % 1.2 0.8 0.1 1.5 1.00 (a)Young's modulus in width direction MPa 6000 6000 6000 5000 5000 ofsupport (b) Young's modulus in longitudinal MPa 8000 8000 8000 6000 6000direction of support (b) − (a) MPa 2000 2000 2000 1000 1000 B μm 0.8 0.40.2 1 0.5 Heat treatment temperature ° C. None None None None NoneBending elastic modulus of reel hub GPa 3 3 3 3 3 material Glass fibercontent of reel hub % 10 10 10 10 10 material Winding tension duringmanufacture 0.50N 0.50N 0.50N 0.50N 0.50N Medium life 1 year 1.5 years 2years 0.5 years 1 year Recording and reproducing 1 1 1 1 1 performanceComparative Comparative Comparative Comparative Unit Example 6 Example 7Example 8 Example 9 Kind of ferromagnetic powder BaFe BaFe BaFe BaFeKind of support PEN PET PET PEN Moisture content of support % 0.1 0.80.8 1.0 (a) Young's modulus in width direction MPa 5000 3000 4000 3000of support (b) Young's modulus in longitudinal MPa 6000 4000 4500 4000direction of support (b) − (a) MPa 1000 1000 500 1000 B μm 0.3 0.8 0.70.8 Heat treatment temperature ° C. None None None None Bending elasticmodulus of reel hub GPa 3 3 3 3 material Glass fiber content of reel hub% 10 10 10 10 material Winding tension during manufacture 0.50N 0.50N0.50N 0.50N Medium life 2 years 1 year 1 year 1 year Recording andreproducing 1 1 1 1 performance

Regarding the magnetic tape cartridge of Example 1, the recording andreproducing performance was evaluated by the method described above,except that the rewinding tension for winding around the cartridge reelwas changed from 0.40 N to 0.50 N in the evaluation of the recording andreproducing performance, and the evaluation result was “2”.

A magnetic tape cartridge was manufactured by the method described aboveas in Example 1 except that the homeotropic alignment process was notperformed in a case of manufacturing the magnetic tape.

A sample piece was cut out from the magnetic tape taken out from themagnetic tape cartridge. For this sample piece, a vertical squarenessratio was obtained by the method described above using aTM-TRVSM5050-SMSL type manufactured by Tamagawa Seisakusho Co., Ltd. asan oscillation sample type magnetic-flux meter and it was 0.55.

The magnetic tape was also taken out from the magnetic tape cartridge ofExample 1, and the vertical squareness ratio was obtained in the samemanner for the sample piece cut out from the magnetic tape, and it was0.60.

The magnetic tapes taken out from the above two magnetic tape cartridgeswere attached to each of the ½-inch reel testers, and theelectromagnetic conversion characteristics (signal-to-noise ratio (SNR))were evaluated by the following methods. As a result, regarding themagnetic tape taken out from the magnetic tape cartridge of Example 1, avalue of SNR 2 dB higher than that of the magnetic tape manufacturedwithout the homeotropic alignment process was obtained.

In an environment of a temperature of 23° C. and a relative humidity of50%, a tension of 0.70 N was applied in the longitudinal direction ofthe magnetic tape, and recording and reproduction were performed for 10passes. A relative speed of the magnetic head and the magnetic tape wasset as 6 m/sec. The recording was performed by using a metal-in-gap(MIG) head (gap length of 0.15 μm, track width of 1.0 μm) as therecording head and by setting a recording current as an optimalrecording current of each magnetic tape. The reproduction was performedusing a giant-magnetoresistive (GMR) head (element thickness of 15 nm,shield interval of 0.1 μm, reproducing element width of 0.8 μm) as thereproduction head. A signal having a linear recording density of 300kfci was recorded, and the reproduced signal was measured with aspectrum analyzer manufactured by ShibaSoku Co., Ltd. In addition, theunit kfci is a unit of linear recording density (cannot be converted toSI unit system). As the signal, a sufficiently stabilized portion of thesignal after starting the running of the magnetic tape was used.

One embodiment of the invention is advantageous in a technical field ofvarious data storages such as archives.

What is claimed is:
 1. A magnetic tape cartridge comprising: a magnetic tape which is wound around a cartridge reel and accommodated in the magnetic tape cartridge, wherein the magnetic tape includes a non-magnetic support, and a magnetic layer containing a ferromagnetic powder, the magnetic layer includes a plurality of servo bands, in a case where a maximum value of an absolute value of a difference between a servo band spacing obtained before storage in an environment of a temperature of 32° C. and relative humidity of 55% and a servo band spacing obtained after storage in the environment for a storage time T is set to A, a unit of A is and T is defined as 24 hours, 48 hours, 72 hours, 96 hours, or 120 hours, a medium life calculated by a linear function of A and a logarithm log_(e)T of T, that are derived from a value of A and a value of the logarithm log_(e)T of T obtained for each T is 3 years or longer, the medium life is T, in a case where A satisfies Equation 1: A=1.5−B, and   (Equation 1) the B is a value calculated by multiplying a difference between a maximum value and a minimum value of the servo band spacings obtained in each of the following five environments of a temperature of 16° C. and relative humidity of 20%, a temperature of 16° C. and relative humidity of 80%, a temperature of 26° C. and relative humidity of 80%, a temperature of 32° C. and relative humidity of 20%, and a temperature 32° C. and relative humidity of 55%, by ½, and the unit is μm.
 2. The magnetic tape cartridge according to claim 1, wherein the T in a case where the A calculated by the linear function satisfies Equation 1 is 3 years to 150 years.
 3. The magnetic tape cartridge according to claim 1, wherein the magnetic tape further includes a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer.
 4. The magnetic tape cartridge according to claim 1, wherein the magnetic tape further includes a back coating layer containing a non-magnetic powder, on a surface side of the non-magnetic support opposite to a surface side provided with the magnetic layer.
 5. The magnetic tape cartridge according to claim 1, wherein the non-magnetic support is an aromatic polyester support.
 6. The magnetic tape cartridge according to claim 5, wherein the aromatic polyester support is a polyethylene terephthalate support.
 7. The magnetic tape cartridge according to claim 5, wherein the aromatic polyester support is a polyethylene naphthalate support.
 8. The magnetic tape cartridge according to claim 1, wherein the non-magnetic support is an aromatic polyamide support.
 9. The magnetic tape cartridge according to claim 1, wherein a vertical squareness ratio of the magnetic tape is 0.60 or more.
 10. A magnetic recording and reproducing device comprising: the magnetic tape cartridge according to claim
 1. 11. The magnetic recording and reproducing device according to claim 10, further comprising: a magnetic head having a reproducing element width of 0.8 μm or less.
 12. The magnetic recording and reproducing device according to claim 10, further comprising: the magnetic tape cartridge; and a winding reel, wherein the magnetic tape is caused to run between the winding reel and a cartridge reel of the magnetic tape cartridge in a state where a tension is applied in a longitudinal direction of the magnetic tape, where a maximum value of the tension is 0.50 N or more, and the magnetic tape after running in the state where the tension is applied is wound around the cartridge reel of the magnetic tape cartridge by applying a tension of 0.40 N or less in the longitudinal direction of the magnetic tape.
 13. The magnetic recording and reproducing device according to claim 10, wherein the T in a case where the A calculated by the linear function satisfies Equation 1 is 3 years to 150 years.
 14. The magnetic recording and reproducing device according to claim 10, wherein the magnetic tape further includes a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer.
 15. The magnetic recording and reproducing device according to claim 10, wherein the magnetic tape further includes a back coating layer containing a non-magnetic powder, on a surface side of the non-magnetic support opposite to a surface side provided with the magnetic layer.
 16. The magnetic recording and reproducing device according to claim 10, wherein the non-magnetic support is an aromatic polyester support.
 17. The magnetic recording and reproducing device according to claim 16, wherein the aromatic polyester support is a polyethylene terephthalate support.
 18. The magnetic recording and reproducing device according to claim 16, wherein the aromatic polyester support is a polyethylene naphthalate support.
 19. The magnetic recording and reproducing device according to claim 10, wherein the non-magnetic support is an aromatic polyamide support.
 20. The magnetic recording and reproducing device according to claim 10, wherein a vertical squareness ratio of the magnetic tape is 0.60 or more. 